[Chrome OS] Add README to explain wonky DEPS file use
[Chrome OS] Add README to explain wonky DEPS file use

We are moving to using a DEPS file for extra chromium os deps that is checked into the main Chromium tree.  As an artifact of the way gclient works, this means that devs will have a r/w version of this file in their source tree and _also_ a read-only version that gclient checks out somewhere else.  This README explains this and how to update the DEPS file correctly.

BUG=None
TEST=None

Review URL: http://codereview.chromium.org/5587011

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@68660 0039d316-1c4b-4281-b951-d872f2087c98

jaruba/chromium.src,keishi/chromium,TheTypoMaster/chromium-crosswalk,robclark/chromium,nacl-webkit/chrome_deps,junmin-zhu/chromium-rivertrail,PeterWangIntel/chromium-crosswalk,nacl-webkit/chrome_deps,hgl888/chromium-crosswalk-efl,rogerwang/chromium,mohamed--abdel-maksoud/chromium.src,M4sse/chromium.src,keishi/chromium,zcbenz/cefode-chromium,nacl-webkit/chrome_deps,hujiajie/pa-chromium,bright-sparks/chromium-spacewalk,Just-D/chromium-1,krieger-od/nwjs_chromium.src,Jonekee/chromium.src,mohamed--abdel-maksoud/chromium.src,junmin-zhu/chromium-rivertrail,nacl-webkit/chrome_deps,junmin-zhu/chromium-rivertrail,ltilve/chromium,robclark/chromium,Just-D/chromium-1,ltilve/chromium,Chilledheart/chromium,patrickm/chromium.src,pozdnyakov/chromium-crosswalk,junmin-zhu/chromium-rivertrail,hujiajie/pa-chromium,Pluto-tv/chromium-crosswalk,timopulkkinen/BubbleFish,PeterWangIntel/chromium-crosswalk,junmin-zhu/chromium-rivertrail,jaruba/chromium.src,zcbenz/cefode-chromium,rogerwang/chromium,Pluto-tv/chromium-crosswalk,robclark/chromium,ltilve/chromium,mogoweb/chromium-crosswalk,dushu1203/chromium.src,Fireblend/chromium-crosswalk,junmin-zhu/chromium-rivertrail,M4sse/chromium.src,ChromiumWebApps/chromium,robclark/chromium,jaruba/chromium.src,hgl888/chromium-crosswalk-efl,littlstar/chromium.src,timopulkkinen/BubbleFish,crosswalk-project/chromium-crosswalk-efl,ChromiumWebApps/chromium,markYoungH/chromium.src,ltilve/chromium,mogoweb/chromium-crosswalk,littlstar/chromium.src,PeterWangIntel/chromium-crosswalk,littlstar/chromium.src,mohamed--abdel-maksoud/chromium.src,krieger-od/nwjs_chromium.src,timopulkkinen/BubbleFish,rogerwang/chromium,pozdnyakov/chromium-crosswalk,nacl-webkit/chrome_deps,anirudhSK/chromium,chuan9/chromium-crosswalk,hujiajie/pa-chromium,bright-sparks/chromium-spacewalk,hgl888/chromium-crosswalk,pozdnyakov/chromium-crosswalk,rogerwang/chromium,timopulkkinen/BubbleFish,Just-D/chromium-1,crosswalk-project/chromium-crosswalk-efl,hgl888/chromium-crosswalk,M4sse/chromium.src,dednal/chromium.src,dednal/chromium.src,patrickm/chromium.src,mohamed--abdel-maksoud/chromium.src,krieger-od/nwjs_chromium.src,anirudhSK/chromium,keishi/chromium,keishi/chromium,TheTypoMaster/chromium-crosswalk,hujiajie/pa-chromium,fujunwei/chromium-crosswalk,axinging/chromium-crosswalk,Just-D/chromium-1,zcbenz/cefode-chromium,nacl-webkit/chrome_deps,mogoweb/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,hgl888/chromium-crosswalk,rogerwang/chromium,hgl888/chromium-crosswalk-efl,robclark/chromium,fujunwei/chromium-crosswalk,pozdnyakov/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Fireblend/chromium-crosswalk,ondra-novak/chromium.src,patrickm/chromium.src,zcbenz/cefode-chromium,hgl888/chromium-crosswalk-efl,PeterWangIntel/chromium-crosswalk,hgl888/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,dednal/chromium.src,Fireblend/chromium-crosswalk,anirudhSK/chromium,ChromiumWebApps/chromium,krieger-od/nwjs_chromium.src,dushu1203/chromium.src,ChromiumWebApps/chromium,dushu1203/chromium.src,keishi/chromium,hgl888/chromium-crosswalk-efl,ChromiumWebApps/chromium,mogoweb/chromium-crosswalk,dushu1203/chromium.src,Fireblend/chromium-crosswalk,markYoungH/chromium.src,dushu1203/chromium.src,robclark/chromium,crosswalk-project/chromium-crosswalk-efl,Chilledheart/chromium,jaruba/chromium.src,bright-sparks/chromium-spacewalk,chuan9/chromium-crosswalk,keishi/chromium,PeterWangIntel/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,mogoweb/chromium-crosswalk,zcbenz/cefode-chromium,rogerwang/chromium,Just-D/chromium-1,jaruba/chromium.src,anirudhSK/chromium,Pluto-tv/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,pozdnyakov/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,Just-D/chromium-1,Jonekee/chromium.src,M4sse/chromium.src,ondra-novak/chromium.src,hgl888/chromium-crosswalk-efl,chuan9/chromium-crosswalk,dushu1203/chromium.src,M4sse/chromium.src,M4sse/chromium.src,Jonekee/chromium.src,PeterWangIntel/chromium-crosswalk,littlstar/chromium.src,fujunwei/chromium-crosswalk,rogerwang/chromium,Jonekee/chromium.src,dushu1203/chromium.src,axinging/chromium-crosswalk,junmin-zhu/chromium-rivertrail,dednal/chromium.src,krieger-od/nwjs_chromium.src,M4sse/chromium.src,bright-sparks/chromium-spacewalk,PeterWangIntel/chromium-crosswalk,markYoungH/chromium.src,ltilve/chromium,mogoweb/chromium-crosswalk,timopulkkinen/BubbleFish,ltilve/chromium,dednal/chromium.src,anirudhSK/chromium,M4sse/chromium.src,Pluto-tv/chromium-crosswalk,robclark/chromium,TheTypoMaster/chromium-crosswalk,littlstar/chromium.src,rogerwang/chromium,chuan9/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,Just-D/chromium-1,pozdnyakov/chromium-crosswalk,axinging/chromium-crosswalk,dednal/chromium.src,dushu1203/chromium.src,ondra-novak/chromium.src,Just-D/chromium-1,keishi/chromium,Chilledheart/chromium,Chilledheart/chromium,ChromiumWebApps/chromium,anirudhSK/chromium,chuan9/chromium-crosswalk,littlstar/chromium.src,Jonekee/chromium.src,Pluto-tv/chromium-crosswalk,rogerwang/chromium,zcbenz/cefode-chromium,M4sse/chromium.src,Jonekee/chromium.src,Pluto-tv/chromium-crosswalk,littlstar/chromium.src,Jonekee/chromium.src,zcbenz/cefode-chromium,anirudhSK/chromium,Jonekee/chromium.src,jaruba/chromium.src,axinging/chromium-crosswalk,junmin-zhu/chromium-rivertrail,markYoungH/chromium.src,axinging/chromium-crosswalk,anirudhSK/chromium,ondra-novak/chromium.src,Jonekee/chromium.src,dushu1203/chromium.src,chuan9/chromium-crosswalk,M4sse/chromium.src,keishi/chromium,axinging/chromium-crosswalk,jaruba/chromium.src,crosswalk-project/chromium-crosswalk-efl,TheTypoMaster/chromium-crosswalk,hgl888/chromium-crosswalk,zcbenz/cefode-chromium,fujunwei/chromium-crosswalk,markYoungH/chromium.src,rogerwang/chromium,TheTypoMaster/chromium-crosswalk,ltilve/chromium,fujunwei/chromium-crosswalk,junmin-zhu/chromium-rivertrail,robclark/chromium,ChromiumWebApps/chromium,mohamed--abdel-maksoud/chromium.src,timopulkkinen/BubbleFish,keishi/chromium,Fireblend/chromium-crosswalk,axinging/chromium-crosswalk,timopulkkinen/BubbleFish,ChromiumWebApps/chromium,robclark/chromium,dednal/chromium.src,patrickm/chromium.src,hgl888/chromium-crosswalk,chuan9/chromium-crosswalk,Jonekee/chromium.src,keishi/chromium,markYoungH/chromium.src,ChromiumWebApps/chromium,anirudhSK/chromium,hujiajie/pa-chromium,patrickm/chromium.src,jaruba/chromium.src,ondra-novak/chromium.src,robclark/chromium,zcbenz/cefode-chromium,nacl-webkit/chrome_deps,hujiajie/pa-chromium,nacl-webkit/chrome_deps,jaruba/chromium.src,timopulkkinen/BubbleFish,patrickm/chromium.src,pozdnyakov/chromium-crosswalk,patrickm/chromium.src,dednal/chromium.src,fujunwei/chromium-crosswalk,markYoungH/chromium.src,krieger-od/nwjs_chromium.src,ondra-novak/chromium.src,krieger-od/nwjs_chromium.src,timopulkkinen/BubbleFish,dednal/chromium.src,ondra-novak/chromium.src,mogoweb/chromium-crosswalk,dednal/chromium.src,bright-sparks/chromium-spacewalk,krieger-od/nwjs_chromium.src,PeterWangIntel/chromium-crosswalk,markYoungH/chromium.src,pozdnyakov/chromium-crosswalk,dushu1203/chromium.src,chuan9/chromium-crosswalk,dednal/chromium.src,Chilledheart/chromium,ltilve/chromium,hgl888/chromium-crosswalk-efl,nacl-webkit/chrome_deps,chuan9/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,krieger-od/nwjs_chromium.src,Chilledheart/chromium,hgl888/chromium-crosswalk-efl,ChromiumWebApps/chromium,mogoweb/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,hgl888/chromium-crosswalk-efl,mohamed--abdel-maksoud/chromium.src,littlstar/chromium.src,crosswalk-project/chromium-crosswalk-efl,zcbenz/cefode-chromium,krieger-od/nwjs_chromium.src,crosswalk-project/chromium-crosswalk-efl,hujiajie/pa-chromium,junmin-zhu/chromium-rivertrail,keishi/chromium,hujiajie/pa-chromium,bright-sparks/chromium-spacewalk,TheTypoMaster/chromium-crosswalk,zcbenz/cefode-chromium,anirudhSK/chromium,bright-sparks/chromium-spacewalk,dushu1203/chromium.src,PeterWangIntel/chromium-crosswalk,fujunwei/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,pozdnyakov/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,hgl888/chromium-crosswalk,ondra-novak/chromium.src,hgl888/chromium-crosswalk-efl,mogoweb/chromium-crosswalk,patrickm/chromium.src,ondra-novak/chromium.src,Fireblend/chromium-crosswalk,Pluto-tv/chromium-crosswalk,hujiajie/pa-chromium,Fireblend/chromium-crosswalk,jaruba/chromium.src,Jonekee/chromium.src,mogoweb/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,ChromiumWebApps/chromium,hgl888/chromium-crosswalk,krieger-od/nwjs_chromium.src,pozdnyakov/chromium-crosswalk,bright-sparks/chromium-spacewalk,axinging/chromium-crosswalk,Fireblend/chromium-crosswalk,markYoungH/chromium.src,hgl888/chromium-crosswalk,nacl-webkit/chrome_deps,mohamed--abdel-maksoud/chromium.src,bright-sparks/chromium-spacewalk,jaruba/chromium.src,anirudhSK/chromium,Chilledheart/chromium,Just-D/chromium-1,Pluto-tv/chromium-crosswalk,markYoungH/chromium.src,ltilve/chromium,Pluto-tv/chromium-crosswalk,timopulkkinen/BubbleFish,pozdnyakov/chromium-crosswalk,fujunwei/chromium-crosswalk,timopulkkinen/BubbleFish,markYoungH/chromium.src,axinging/chromium-crosswalk,junmin-zhu/chromium-rivertrail,anirudhSK/chromium,fujunwei/chromium-crosswalk,Fireblend/chromium-crosswalk,M4sse/chromium.src,patrickm/chromium.src,hujiajie/pa-chromium,hujiajie/pa-chromium,ChromiumWebApps/chromium,nacl-webkit/chrome_deps