Fix headings in stream-events documentation
Fix headings in stream-events documentation

Decrease the heading level of the "Events" section and subsections,
so that all the events are listed in the table of contents.

Change-Id: I7b98d913eb2f651be5a66bb1b23d95f981107fe0

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