Clarify that documentation for plugins has to be in pegdown
Clarify that documentation for plugins has to be in pegdown

To avoid that plugin developers write documentation in the wrong
Markdown flavor, we make the used flavor explicit in the
documentation.

Change-Id: Id04c693294ba6dd396796a8c423a7d9c9890c18a

quyixia/gerrit,renchaorevee/gerrit,qtproject/qtqa-gerrit,MerritCR/merrit,jackminicloud/test,qtproject/qtqa-gerrit,jackminicloud/test,joshuawilson/merrit,qtproject/qtqa-gerrit,pkdevbox/gerrit,WANdisco/gerrit,gerrit-review/gerrit,pkdevbox/gerrit,MerritCR/merrit,joshuawilson/merrit,jackminicloud/test,Seinlin/gerrit,TonyChai24/test,TonyChai24/test,GerritCodeReview/gerrit,renchaorevee/gerrit,MerritCR/merrit,MerritCR/merrit,qtproject/qtqa-gerrit,TonyChai24/test,thesamet/gerrit,hdost/gerrit,Distrotech/gerrit,MerritCR/merrit,Seinlin/gerrit,hdost/gerrit,supriyantomaftuh/gerrit,gerrit-review/gerrit,pkdevbox/gerrit,supriyantomaftuh/gerrit,Seinlin/gerrit,renchaorevee/gerrit,netroby/gerrit,WANdisco/gerrit,gerrit-review/gerrit,WANdisco/gerrit,qtproject/qtqa-gerrit,joshuawilson/merrit,netroby/gerrit,hdost/gerrit,joshuawilson/merrit,gerrit-review/gerrit,hdost/gerrit,TonyChai24/test,TonyChai24/test,GerritCodeReview/gerrit,quyixia/gerrit,jackminicloud/test,GerritCodeReview/gerrit,joshuawilson/merrit,thesamet/gerrit,Distrotech/gerrit,netroby/gerrit,netroby/gerrit,thesamet/gerrit,MerritCR/merrit,MerritCR/merrit,quyixia/gerrit,supriyantomaftuh/gerrit,Seinlin/gerrit,renchaorevee/gerrit,Distrotech/gerrit,thesamet/gerrit,Seinlin/gerrit,gerrit-review/gerrit,qtproject/qtqa-gerrit,GerritCodeReview/gerrit,supriyantomaftuh/gerrit,supriyantomaftuh/gerrit,renchaorevee/gerrit,supriyantomaftuh/gerrit,joshuawilson/merrit,quyixia/gerrit,renchaorevee/gerrit,TonyChai24/test,gerrit-review/gerrit,joshuawilson/merrit,Distrotech/gerrit,supriyantomaftuh/gerrit,hdost/gerrit,pkdevbox/gerrit,hdost/gerrit,renchaorevee/gerrit,Seinlin/gerrit,netroby/gerrit,gerrit-review/gerrit,jackminicloud/test,thesamet/gerrit,Distrotech/gerrit,WANdisco/gerrit,quyixia/gerrit,netroby/gerrit,WANdisco/gerrit,GerritCodeReview/gerrit,jackminicloud/test,jackminicloud/test,WANdisco/gerrit,netroby/gerrit,hdost/gerrit,thesamet/gerrit,quyixia/gerrit,WANdisco/gerrit,quyixia/gerrit,GerritCodeReview/gerrit,Seinlin/gerrit,Distrotech/gerrit,pkdevbox/gerrit,pkdevbox/gerrit,pkdevbox/gerrit,joshuawilson/merrit,GerritCodeReview/gerrit,Distrotech/gerrit,GerritCodeReview/gerrit,MerritCR/merrit,qtproject/qtqa-gerrit,thesamet/gerrit,TonyChai24/test