Add references to issue subscription/notification

Users reporting or looking at issues commonly want to know to get
notified about updates on the issue. We had a pointer to the overall
issue tracker docs, but adding pointers for this specific case will
improve the user experience based on user summit feedback.

Feature: Issue 40013919
Change-Id: I3b7fdeede6b52cdff74170dbfe95b1f5f7baec2c
2 files changed