[doc] Fix release notes formatting

Change-Id: I297418f17ce0a5e60c1560daba19381ca5aa58f5
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>
[427273] Replace auto-generated help index with a nice-looking page

Bug: 427273
Change-Id: I3e664bc78cc8b931a06903494b71cfea42b5e447
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>