Mark project and user options as required for LsUserRefs

The documentation of, and the 'ssh ... --help' page for LsUserRefs
showed the project and user options as optional although they were
required. We now mark them as required in their annotations. Thereby,
the 'ssh ... --help' page lists them as required, and it is
automatically assured that they are not null. We also marked them as
required in the documentation.

Change-Id: I73aace6eeebb897174628c444350a275b323b673
diff --git a/Documentation/cmd-ls-user-refs.txt b/Documentation/cmd-ls-user-refs.txt
index c0e072d..785a7c3 100644
--- a/Documentation/cmd-ls-user-refs.txt
+++ b/Documentation/cmd-ls-user-refs.txt
@@ -31,11 +31,11 @@
 -------
 --project::
 -p::
-	Name of the project for which the refs should be listed.
+	Required; Name of the project for which the refs should be listed.
 
 --user::
 -u::
-	User for which the visible refs should be listed. Gerrit
+	Required; User for which the visible refs should be listed. Gerrit
 	will query the database to find matching users, so the
 	full identity/name does not need to be specified.