Finalise Gerrit v3.4.6 release notes
Finalise Gerrit v3.4.6 release notes

Change-Id: I806a3ad58adf526b79835aabd5d86f549ef2a91c

GerritCodeReview/homepage,GerritCodeReview/homepage,GerritCodeReview/homepage,GerritCodeReview/homepage,GerritCodeReview/homepage