Update developer instructions for cloning the Gerrit project
Update developer instructions for cloning the Gerrit project

The core plugins are now included as git submodules.

When cloning the gerrit project, the --recursive option must be
used otherwise the submodules will not be cloned and the build
will not work.

Update the documentation accordingly.

Change-Id: I02decd68a1de061b60d3e7b6ce2ffdd24d12505a
(cherry picked from commit 4f2be538e7fa9f5ab67edf963615bd721a027285)
MerritCR/merrit,quyixia/gerrit,renchaorevee/gerrit,bootstraponline-archive/gerrit-mirror,thesamet/gerrit,dwhipstock/gerrit,gcoders/gerrit,pkdevbox/gerrit,hdost/gerrit,basilgor/gerrit,MerritCR/merrit,Distrotech/gerrit,Seinlin/gerrit,anminhsu/gerrit,jackminicloud/test,anminhsu/gerrit,ckamm/gerrit,Team-OctOS/host_gerrit,ckamm/gerrit,anminhsu/gerrit,supriyantomaftuh/gerrit,thesamet/gerrit,supriyantomaftuh/gerrit,WANdisco/gerrit,zommarin/gerrit,quyixia/gerrit,dwhipstock/gerrit,bpollack/gerrit,thesamet/gerrit,Overruler/gerrit,quyixia/gerrit,gerrit-review/gerrit,Distrotech/gerrit,zommarin/gerrit,MerritCR/merrit,joshuawilson/merrit,gracefullife/gerrit,WANdisco/gerrit,supriyantomaftuh/gerrit,Team-OctOS/host_gerrit,gerrit-review/gerrit,GerritCodeReview/gerrit,basilgor/gerrit,Seinlin/gerrit,GerritCodeReview/gerrit,thesamet/gerrit,pkdevbox/gerrit,WANdisco/gerrit,MerritCR/merrit,WANdisco/gerrit,gerrit-review/gerrit,joshuawilson/merrit,gcoders/gerrit,supriyantomaftuh/gerrit,thesamet/gerrit,thinkernel/gerrit,gcoders/gerrit,MerritCR/merrit,qtproject/qtqa-gerrit,TonyChai24/test,anminhsu/gerrit,basilgor/gerrit,thesamet/gerrit,Overruler/gerrit,gerrit-review/gerrit,GerritCodeReview/gerrit,Distrotech/gerrit,TonyChai24/test,ckamm/gerrit,Team-OctOS/host_gerrit,Team-OctOS/host_gerrit,quyixia/gerrit,gcoders/gerrit,Saulis/gerrit,thinkernel/gerrit,Saulis/gerrit,hdost/gerrit,midnightradio/gerrit,quyixia/gerrit,Seinlin/gerrit,zommarin/gerrit,renchaorevee/gerrit,joshuawilson/merrit,Distrotech/gerrit,jackminicloud/test,thinkernel/gerrit,Distrotech/gerrit,joshuawilson/merrit,jackminicloud/test,qtproject/qtqa-gerrit,Seinlin/gerrit,bootstraponline-archive/gerrit-mirror,netroby/gerrit,GerritCodeReview/gerrit,dwhipstock/gerrit,hdost/gerrit,Distrotech/gerrit,gcoders/gerrit,bpollack/gerrit,thinkernel/gerrit,gracefullife/gerrit,bpollack/gerrit,supriyantomaftuh/gerrit,qtproject/qtqa-gerrit,TonyChai24/test,TonyChai24/test,Distrotech/gerrit,Saulis/gerrit,joshuawilson/merrit,MerritCR/merrit,pkdevbox/gerrit,Overruler/gerrit,dwhipstock/gerrit,basilgor/gerrit,netroby/gerrit,GerritCodeReview/gerrit,dwhipstock/gerrit,qtproject/qtqa-gerrit,hdost/gerrit,hdost/gerrit,jackminicloud/test,anminhsu/gerrit,basilgor/gerrit,Team-OctOS/host_gerrit,GerritCodeReview/gerrit,bpollack/gerrit,pkdevbox/gerrit,netroby/gerrit,Team-OctOS/host_gerrit,anminhsu/gerrit,dwhipstock/gerrit,netroby/gerrit,renchaorevee/gerrit,gerrit-review/gerrit,bootstraponline-archive/gerrit-mirror,bootstraponline-archive/gerrit-mirror,thesamet/gerrit,jackminicloud/test,bpollack/gerrit,ckamm/gerrit,ckamm/gerrit,renchaorevee/gerrit,bootstraponline-archive/gerrit-mirror,renchaorevee/gerrit,jackminicloud/test,gerrit-review/gerrit,Overruler/gerrit,gerrit-review/gerrit,midnightradio/gerrit,qtproject/qtqa-gerrit,zommarin/gerrit,WANdisco/gerrit,zommarin/gerrit,Team-OctOS/host_gerrit,gcoders/gerrit,Seinlin/gerrit,supriyantomaftuh/gerrit,bpollack/gerrit,renchaorevee/gerrit,Seinlin/gerrit,jackminicloud/test,midnightradio/gerrit,GerritCodeReview/gerrit,qtproject/qtqa-gerrit,quyixia/gerrit,midnightradio/gerrit,gracefullife/gerrit,qtproject/qtqa-gerrit,TonyChai24/test,Saulis/gerrit,MerritCR/merrit,gcoders/gerrit,netroby/gerrit,hdost/gerrit,Overruler/gerrit,Overruler/gerrit,pkdevbox/gerrit,bootstraponline-archive/gerrit-mirror,anminhsu/gerrit,joshuawilson/merrit,joshuawilson/merrit,Saulis/gerrit,supriyantomaftuh/gerrit,GerritCodeReview/gerrit,Saulis/gerrit,TonyChai24/test,WANdisco/gerrit,Seinlin/gerrit,dwhipstock/gerrit,thinkernel/gerrit,netroby/gerrit,gracefullife/gerrit,WANdisco/gerrit,thinkernel/gerrit,netroby/gerrit,MerritCR/merrit,thinkernel/gerrit,midnightradio/gerrit,renchaorevee/gerrit,quyixia/gerrit,joshuawilson/merrit,gracefullife/gerrit,pkdevbox/gerrit,midnightradio/gerrit,pkdevbox/gerrit,hdost/gerrit,TonyChai24/test