Merge branch 'tk/ambiguous-fetch-refspec'

Give hint when branch tracking cannot be established because fetch
refspecs from multiple remote repositories overlap.

* tk/ambiguous-fetch-refspec:
  tracking branches: add advice to ambiguous refspec error

Documentation/config/advice.txt

@@ -4,6 +4,10 @@ advice.*::
 	can tell Git that you do not need help by setting these to 'false':
 +
 --
+	ambiguousFetchRefspec::
+		Advice shown when fetch refspec for multiple remotes map to
+		the same remote-tracking branch namespace and causes branch
+		tracking set-up to fail.
 	fetchShowForcedUpdates::
 		Advice shown when linkgit:git-fetch[1] takes a long time
 		to calculate forced updates after ref updates, or to warn