Update doc with format to set multiple votes on push

The docs[1] say that you should be able to set multiple labels
when uploading new patchsets to gerrit however it's not clear
what the format is required to do that.  Add an example to
make it clearer.

[1] https://gerrit-review.googlesource.com/Documentation/
       user-upload.html#review_labels

Change-Id: I90d8b58534c2272a41a4a8ac800ba84215274d13
diff --git a/Documentation/user-upload.txt b/Documentation/user-upload.txt
index 5c23ce8..6152f24 100644
--- a/Documentation/user-upload.txt
+++ b/Documentation/user-upload.txt
@@ -189,6 +189,10 @@
 The `l='label[score]'` option may be specified more than once to
 apply multiple review labels.
 
+====
+  git push ssh://john.doe@git.example.com:29418/kernel/common HEAD:refs/for/experimental%l=Code-Review+1,l=Verified+1
+====
+
 The value is optional.  If not specified, it defaults to +1 (if
 the label range allows it).