Added explanation for "One or more refs/for/ ..." error

Added a documentation page that explains the
"One or more refs/for/ names blocks change upload"
error and what can be done to solve the problem.

Change-Id: I11dc3c72afcd600b1f5d4fdbed44a0d5278b0da3
Signed-off-by: Edwin Kempin <edwin.kempin@gmail.com>
diff --git a/Documentation/error-messages.txt b/Documentation/error-messages.txt
index 2f0a8f2..6091af3 100644
--- a/Documentation/error-messages.txt
+++ b/Documentation/error-messages.txt
@@ -17,6 +17,7 @@
 * link:error-no-new-changes.html[no new changes]
 * link:error-not-a-gerrit-project.html[not a Gerrit project]
 * link:error-not-valid-ref.html[not valid ref]
+* link:error-change-upload-blocked.html[One or more refs/for/ names blocks change upload]
 * link:error-permission-denied.html[Permission denied (publickey)]
 * link:error-prohibited-by-gerrit.html[prohibited by Gerrit]
 * link:error-squash-commits-first.html[squash commits first]