Add new ACL for abandoning changes

Bug: Issue 930
Change-Id: I9275cc8de218953dc9f5c211f0c60e8008b8efb9

Documentation/access-control.txt

diff --git a/Documentation/access-control.txt b/Documentation/access-control.txt
index b9fb8b3..ad20cb3 100644
--- a/Documentation/access-control.txt
+++ b/Documentation/access-control.txt
@@ -444,6 +444,14 @@
 A restart is required after making database changes.
 See <<restart_changes,below>>.
 
+[[category_abandon]]
+Abandon
+~~~~
+
+This category controls whether users are allowed to abandon changes
+to projects in Gerrit. It can give permission to abandon a specific
+change to a given ref.
+
 [[category_create]]
 Create reference
 ~~~~~~~~~~~~~~~~