Update gerrit flush-caches documentation about web_sessions
Update gerrit flush-caches documentation about web_sessions

The web_sessions cache is not flushed automatically, because doing so
would throw existing users off.  We should mention this, as its useful
for the administrator to know that we've already considered this case
and aren't going to make it easy to break the active users.

Signed-off-by: Shawn O. Pearce <f3ea74d906fa9fe97c1fef6bad9cb871485c7045@google.com>

anminhsu/gerrit,jackminicloud/test,supriyantomaftuh/gerrit,gcoders/gerrit,1yvT0s/gerrit,jeblair/gerrit,hdost/gerrit,renchaorevee/gerrit,MerritCR/merrit,sudosurootdev/gerrit,jackminicloud/test,zommarin/gerrit,atdt/gerrit,Seinlin/gerrit,Saulis/gerrit,skurfuerst/gerrit,pkdevbox/gerrit,renchaorevee/gerrit,MerritCR/merrit,joshuawilson/merrit,skurfuerst/gerrit,ashang/aaron-gerrit,jackminicloud/test,GerritCodeReview/gerrit,GerritCodeReview/gerrit-attic,gcoders/gerrit,pkdevbox/gerrit,hdost/gerrit,basilgor/gerrit,ckamm/gerrit,cjh1/gerrit,joshuawilson/merrit,CandyShop/gerrit,quyixia/gerrit,bpollack/gerrit,zommarin/gerrit,Distrotech/gerrit,quyixia/gerrit,austinchic/Gerrit,ashang/aaron-gerrit,WANdisco/gerrit,Team-OctOS/host_gerrit,hdost/gerrit,teamblueridge/gerrit,Team-OctOS/host_gerrit,CandyShop/gerrit,evanchueng/gerrit,qtproject/qtqa-gerrit,1yvT0s/gerrit,pkdevbox/gerrit,ckamm/gerrit,austinchic/Gerrit,Team-OctOS/host_gerrit,CandyShop/gerrit,hdost/gerrit,jeblair/gerrit,bootstraponline-archive/gerrit-mirror,thinkernel/gerrit,hdost/gerrit,supriyantomaftuh/gerrit,quyixia/gerrit,thesamet/gerrit,duboisf/gerrit,ashang/aaron-gerrit,quyixia/gerrit,renchaorevee/gerrit,gcoders/gerrit,keerath/gerrit_newssh,midnightradio/gerrit,supriyantomaftuh/gerrit,gcoders/gerrit,MerritCR/merrit,skurfuerst/gerrit,midnightradio/gerrit,WANdisco/gerrit,cjh1/gerrit,qtproject/qtqa-gerrit,sudosurootdev/gerrit,teamblueridge/gerrit,thinkernel/gerrit,ckamm/gerrit,teamblueridge/gerrit,gracefullife/gerrit,teamblueridge/gerrit,GerritCodeReview/gerrit,ashang/aaron-gerrit,GerritCodeReview/gerrit-attic,Distrotech/gerrit,makholm/gerrit-ceremony,renchaorevee/gerrit,rtyley/mini-git-server,Distrotech/gerrit,Saulis/gerrit,1yvT0s/gerrit,jeblair/gerrit,zommarin/gerrit,bootstraponline-archive/gerrit-mirror,bpollack/gerrit,basilgor/gerrit,Saulis/gerrit,Saulis/gerrit,joshuawilson/merrit,ckamm/gerrit,CandyShop/gerrit,jackminicloud/test,basilgor/gerrit,midnightradio/gerrit,thinkernel/gerrit,jackminicloud/test,MerritCR/merrit,duboisf/gerrit,dwhipstock/gerrit,gracefullife/gerrit,atdt/gerrit,anminhsu/gerrit,midnightradio/gerrit,TonyChai24/test,bpollack/gerrit,sudosurootdev/gerrit,cjh1/gerrit,dwhipstock/gerrit,WANdisco/gerrit,supriyantomaftuh/gerrit,pkdevbox/gerrit,catrope/gerrit,keerath/gerrit_newssh,anminhsu/gerrit,zommarin/gerrit,joshuawilson/merrit,MerritCR/merrit,jackminicloud/test,Team-OctOS/host_gerrit,Distrotech/gerrit,Saulis/gerrit,gerrit-review/gerrit,makholm/gerrit-ceremony,anminhsu/gerrit,jeblair/gerrit,dwhipstock/gerrit,sudosurootdev/gerrit,pkdevbox/gerrit,midnightradio/gerrit,basilgor/gerrit,netroby/gerrit,bpollack/gerrit,thinkernel/gerrit,Overruler/gerrit,Team-OctOS/host_gerrit,renchaorevee/gerrit,jackminicloud/test,qtproject/qtqa-gerrit,hdost/gerrit,MerritCR/merrit,duboisf/gerrit,thesamet/gerrit,thesamet/gerrit,Team-OctOS/host_gerrit,GerritCodeReview/gerrit,thesamet/gerrit,makholm/gerrit-ceremony,gerrit-review/gerrit,supriyantomaftuh/gerrit,WANdisco/gerrit,GerritCodeReview/gerrit,anminhsu/gerrit,gerrit-review/gerrit,Overruler/gerrit,m1kah/gerrit-contributions,1yvT0s/gerrit,m1kah/gerrit-contributions,TonyChai24/test,thesamet/gerrit,gcoders/gerrit,Seinlin/gerrit,gerrit-review/gerrit,supriyantomaftuh/gerrit,Overruler/gerrit,Distrotech/gerrit,supriyantomaftuh/gerrit,gracefullife/gerrit,evanchueng/gerrit,1yvT0s/gerrit,netroby/gerrit,WANdisco/gerrit,TonyChai24/test,bootstraponline-archive/gerrit-mirror,Team-OctOS/host_gerrit,renchaorevee/gerrit,gerrit-review/gerrit,TonyChai24/test,gcoders/gerrit,m1kah/gerrit-contributions,gerrit-review/gerrit,Overruler/gerrit,catrope/gerrit,sudosurootdev/gerrit,bpollack/gerrit,bootstraponline-archive/gerrit-mirror,GerritCodeReview/gerrit,teamblueridge/gerrit,bootstraponline-archive/gerrit-mirror,CandyShop/gerrit,WANdisco/gerrit,Saulis/gerrit,evanchueng/gerrit,WANdisco/gerrit,joshuawilson/merrit,qtproject/qtqa-gerrit,thinkernel/gerrit,evanchueng/gerrit,catrope/gerrit,dwhipstock/gerrit,bootstraponline-archive/gerrit-mirror,m1kah/gerrit-contributions,netroby/gerrit,GerritCodeReview/gerrit,Seinlin/gerrit,keerath/gerrit_newssh,netroby/gerrit,joshuawilson/merrit,cjh1/gerrit,keerath/gerrit_newssh,GerritCodeReview/gerrit,Seinlin/gerrit,gracefullife/gerrit,TonyChai24/test,qtproject/qtqa-gerrit,atdt/gerrit,dwhipstock/gerrit,Seinlin/gerrit,MerritCR/merrit,dwhipstock/gerrit,renchaorevee/gerrit,anminhsu/gerrit,anminhsu/gerrit,evanchueng/gerrit,GerritCodeReview/gerrit,thesamet/gerrit,Seinlin/gerrit,netroby/gerrit,ckamm/gerrit,austinchic/Gerrit,Overruler/gerrit,hdost/gerrit,basilgor/gerrit,Overruler/gerrit,skurfuerst/gerrit,netroby/gerrit,Seinlin/gerrit,MerritCR/merrit,TonyChai24/test,austinchic/Gerrit,quyixia/gerrit,netroby/gerrit,ashang/aaron-gerrit,TonyChai24/test,Distrotech/gerrit,gracefullife/gerrit,qtproject/qtqa-gerrit,dwhipstock/gerrit,thinkernel/gerrit,catrope/gerrit,GerritCodeReview/gerrit-attic,keerath/gerrit_newssh,atdt/gerrit,zommarin/gerrit,midnightradio/gerrit,quyixia/gerrit,qtproject/qtqa-gerrit,pkdevbox/gerrit,joshuawilson/merrit,gcoders/gerrit,duboisf/gerrit,joshuawilson/merrit,thinkernel/gerrit,pkdevbox/gerrit,thesamet/gerrit,rtyley/mini-git-server,gerrit-review/gerrit,makholm/gerrit-ceremony,atdt/gerrit,Distrotech/gerrit,bpollack/gerrit,quyixia/gerrit