documentation: Update access control for new ref syntaxes
documentation: Update access control for new ref syntaxes

We now support ${username} variables and regular expressions,
so try to document their use a bit.

Change-Id: I3c42fd59b00094eee745de827055794823021618
Signed-off-by: Shawn O. Pearce <f3ea74d906fa9fe97c1fef6bad9cb871485c7045@google.com>

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