Add some more doc for TagSet
Add some more doc for TagSet

Still missing javadoc for TagSetHolder and TagMatcher.

Change-Id: I9a6634084908a94f2a17372db05646391cd00fbf

GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit