Document that the Push ACL is needed for image upload, too

Tested on a snapshot of 2.11; this is needed for proper functionality
with default ACLs and a separate All-Images.git repo for non-Admin
users.

Change-Id: I20bdf974a0c9327f92814f03744da448eb9b2955

src/main/resources/Documentation/about.md

diff --git a/src/main/resources/Documentation/about.md b/src/main/resources/Documentation/about.md
index de447b1..ab89d44 100644
--- a/src/main/resources/Documentation/about.md
+++ b/src/main/resources/Documentation/about.md
@@ -17,7 +17,8 @@
 * [Read](../../../Documentation/access-control.html#category_read) to
   enable users to see the uploaded images.
 
-* [Create Reference](../../../Documentation/access-control.html#category_create)
+* Both [Create Reference](../../../Documentation/access-control.html#category_create)
+  and [Push](../../../Documentation/access-control.html#category_push)
   to enable users to upload images.
 
 In addition Gerrit must be