Update the Maven plugin installation instructions
Update the Maven plugin installation instructions

In Eclipse 3.7 (Indigo) and later, the Maven plugins are available
in the default update site.  It's only necessary to manually add
the m2eclipse update site if using an older version of Eclipse.

Update the documentation accordingly.

Change-Id: Ib109b056313682f954a74344cf0a25bd94d493b5

hdost/gerrit,jackminicloud/test,basilgor/gerrit,bpollack/gerrit,netroby/gerrit,anminhsu/gerrit,gracefullife/gerrit,bpollack/gerrit,Distrotech/gerrit,thesamet/gerrit,quyixia/gerrit,GerritCodeReview/gerrit,Saulis/gerrit,Overruler/gerrit,MerritCR/merrit,Distrotech/gerrit,Team-OctOS/host_gerrit,thesamet/gerrit,Seinlin/gerrit,dwhipstock/gerrit,anminhsu/gerrit,dwhipstock/gerrit,jackminicloud/test,qtproject/qtqa-gerrit,bootstraponline-archive/gerrit-mirror,MerritCR/merrit,TonyChai24/test,jackminicloud/test,netroby/gerrit,hdost/gerrit,basilgor/gerrit,WANdisco/gerrit,dwhipstock/gerrit,qtproject/qtqa-gerrit,ckamm/gerrit,jackminicloud/test,MerritCR/merrit,renchaorevee/gerrit,GerritCodeReview/gerrit,gerrit-review/gerrit,GerritCodeReview/gerrit,thesamet/gerrit,jackminicloud/test,gcoders/gerrit,Team-OctOS/host_gerrit,renchaorevee/gerrit,thinkernel/gerrit,MerritCR/merrit,GerritCodeReview/gerrit,ckamm/gerrit,Distrotech/gerrit,TonyChai24/test,midnightradio/gerrit,WANdisco/gerrit,Seinlin/gerrit,qtproject/qtqa-gerrit,hdost/gerrit,MerritCR/merrit,netroby/gerrit,bootstraponline-archive/gerrit-mirror,dwhipstock/gerrit,ckamm/gerrit,hdost/gerrit,gcoders/gerrit,Distrotech/gerrit,gcoders/gerrit,zommarin/gerrit,gracefullife/gerrit,quyixia/gerrit,pkdevbox/gerrit,qtproject/qtqa-gerrit,Team-OctOS/host_gerrit,Team-OctOS/host_gerrit,gcoders/gerrit,jackminicloud/test,joshuawilson/merrit,quyixia/gerrit,qtproject/qtqa-gerrit,joshuawilson/merrit,gcoders/gerrit,teamblueridge/gerrit,Distrotech/gerrit,anminhsu/gerrit,thinkernel/gerrit,zommarin/gerrit,joshuawilson/merrit,midnightradio/gerrit,MerritCR/merrit,renchaorevee/gerrit,zommarin/gerrit,TonyChai24/test,hdost/gerrit,pkdevbox/gerrit,ckamm/gerrit,gracefullife/gerrit,hdost/gerrit,basilgor/gerrit,Saulis/gerrit,gerrit-review/gerrit,WANdisco/gerrit,ckamm/gerrit,WANdisco/gerrit,Seinlin/gerrit,Team-OctOS/host_gerrit,dwhipstock/gerrit,Overruler/gerrit,thinkernel/gerrit,anminhsu/gerrit,Team-OctOS/host_gerrit,supriyantomaftuh/gerrit,joshuawilson/merrit,renchaorevee/gerrit,supriyantomaftuh/gerrit,hdost/gerrit,thinkernel/gerrit,MerritCR/merrit,jackminicloud/test,bootstraponline-archive/gerrit-mirror,gcoders/gerrit,bpollack/gerrit,Distrotech/gerrit,midnightradio/gerrit,GerritCodeReview/gerrit,netroby/gerrit,zommarin/gerrit,gracefullife/gerrit,WANdisco/gerrit,midnightradio/gerrit,supriyantomaftuh/gerrit,Seinlin/gerrit,TonyChai24/test,supriyantomaftuh/gerrit,thinkernel/gerrit,pkdevbox/gerrit,gerrit-review/gerrit,supriyantomaftuh/gerrit,gerrit-review/gerrit,quyixia/gerrit,gerrit-review/gerrit,teamblueridge/gerrit,zommarin/gerrit,thesamet/gerrit,Team-OctOS/host_gerrit,thesamet/gerrit,thesamet/gerrit,TonyChai24/test,netroby/gerrit,basilgor/gerrit,Distrotech/gerrit,thinkernel/gerrit,joshuawilson/merrit,Overruler/gerrit,TonyChai24/test,GerritCodeReview/gerrit,Saulis/gerrit,GerritCodeReview/gerrit,Saulis/gerrit,Seinlin/gerrit,qtproject/qtqa-gerrit,quyixia/gerrit,WANdisco/gerrit,Overruler/gerrit,anminhsu/gerrit,supriyantomaftuh/gerrit,gerrit-review/gerrit,bpollack/gerrit,Overruler/gerrit,midnightradio/gerrit,gcoders/gerrit,GerritCodeReview/gerrit,netroby/gerrit,WANdisco/gerrit,netroby/gerrit,bpollack/gerrit,teamblueridge/gerrit,anminhsu/gerrit,renchaorevee/gerrit,dwhipstock/gerrit,dwhipstock/gerrit,bootstraponline-archive/gerrit-mirror,Overruler/gerrit,teamblueridge/gerrit,teamblueridge/gerrit,pkdevbox/gerrit,anminhsu/gerrit,TonyChai24/test,pkdevbox/gerrit,bootstraponline-archive/gerrit-mirror,gerrit-review/gerrit,Seinlin/gerrit,Saulis/gerrit,Seinlin/gerrit,midnightradio/gerrit,basilgor/gerrit,thinkernel/gerrit,supriyantomaftuh/gerrit,pkdevbox/gerrit,quyixia/gerrit,quyixia/gerrit,renchaorevee/gerrit,bootstraponline-archive/gerrit-mirror,bpollack/gerrit,MerritCR/merrit,renchaorevee/gerrit,Saulis/gerrit,pkdevbox/gerrit,joshuawilson/merrit,qtproject/qtqa-gerrit,thesamet/gerrit,joshuawilson/merrit,joshuawilson/merrit,gracefullife/gerrit