Add some notes about FreeBSD.
Add some notes about FreeBSD.

unkadoug/libunwind,android-ia/platform_external_libunwind,jrmuizel/libunwind,android-ia/platform_external_libunwind,fdoray/libunwind,igprof/libunwind,mpercy/libunwind,djwatson/libunwind,evaautomation/libunwind,Chilledheart/libunwind,djwatson/libunwind,joyent/libunwind,zliu2014/libunwind-tilegx,cms-externals/libunwind,0xlab/0xdroid-external_libunwind,lat/libunwind,krytarowski/libunwind,yuyichao/libunwind,Keno/libunwind,fdoray/libunwind,krytarowski/libunwind,frida/libunwind,ehsan/libunwind,tony/libunwind,fillexen/libunwind,0xlab/0xdroid-external_libunwind,SyndicateRogue/libunwind,frida/libunwind,Keno/libunwind,geekboxzone/mmallow_external_libunwind,libunwind/libunwind,pathscale/libunwind,joyent/libunwind,geekboxzone/lollipop_external_libunwind,atanasyan/libunwind,rantala/libunwind,bo-on-software/libunwind,maltek/platform_external_libunwind,androidarmv6/android_external_libunwind,adsharma/libunwind,igprof/libunwind,project-zerus/libunwind,zliu2014/libunwind-tilegx,ehsan/libunwind,pathscale/libunwind,Chilledheart/libunwind,martyone/libunwind,cms-externals/libunwind,rantala/libunwind,olibc/libunwind,zliu2014/libunwind-tilegx,unkadoug/libunwind,rntz/libunwind,bo-on-software/libunwind,geekboxzone/lollipop_external_libunwind,maltek/platform_external_libunwind,dropbox/libunwind,dropbox/libunwind,vegard/libunwind,androidarmv6/android_external_libunwind,evaautomation/libunwind,bo-on-software/libunwind,olibc/libunwind,maltek/platform_external_libunwind,vtjnash/libunwind,rntz/libunwind,wdv4758h/libunwind,zeldin/platform_external_libunwind,rogwfu/libunwind,vtjnash/libunwind,tkelman/libunwind,atanasyan/libunwind,unkadoug/libunwind,rogwfu/libunwind,olibc/libunwind,Chilledheart/libunwind,atanasyan/libunwind,dreal-deps/libunwind,tkelman/libunwind,CyanogenMod/android_external_libunwind,cloudius-systems/libunwind,libunwind/libunwind,dagar/libunwind,dreal-deps/libunwind,zeldin/platform_external_libunwind,vegard/libunwind,android-ia/platform_external_libunwind,CyanogenMod/android_external_libunwind,mpercy/libunwind,cms-externals/libunwind,DroidSim/platform_external_libunwind,adsharma/libunwind,tronical/libunwind,atanasyan/libunwind-android,adsharma/libunwind,dropbox/libunwind,zeldin/platform_external_libunwind,rogwfu/libunwind,ehsan/libunwind,tkelman/libunwind,geekboxzone/lollipop_external_libunwind,vegard/libunwind,tony/libunwind,martyone/libunwind,libunwind/libunwind,geekboxzone/mmallow_external_libunwind,dreal-deps/libunwind,CyanogenMod/android_external_libunwind,joyent/libunwind,rantala/libunwind,frida/libunwind,rntz/libunwind,tronical/libunwind,Keno/libunwind,lat/libunwind,wdv4758h/libunwind,igprof/libunwind,0xlab/0xdroid-external_libunwind,atanasyan/libunwind-android,DroidSim/platform_external_libunwind,pathscale/libunwind,krytarowski/libunwind,jrmuizel/libunwind,jrmuizel/libunwind,dagar/libunwind,dagar/libunwind,atanasyan/libunwind-android,geekboxzone/mmallow_external_libunwind,djwatson/libunwind,fdoray/libunwind,project-zerus/libunwind,lat/libunwind,tony/libunwind,martyone/libunwind,cloudius-systems/libunwind,evaautomation/libunwind,project-zerus/libunwind,SyndicateRogue/libunwind,cloudius-systems/libunwind,DroidSim/platform_external_libunwind,yuyichao/libunwind,vtjnash/libunwind,tronical/libunwind,yuyichao/libunwind,fillexen/libunwind,fillexen/libunwind,wdv4758h/libunwind,mpercy/libunwind,androidarmv6/android_external_libunwind,SyndicateRogue/libunwind