Document how to get the groups of a user via REST

Change-Id: Ie6d32c8e14d2d4db842c74eb6669a0e9302813d4
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

Documentation/rest-api-accounts.txt

@@ -137,6 +137,65 @@ If the user doesn't have the global capability the response is
 get::/accounts/self/capabilities/createGroup
 ****
 
+[[list-groups]]
+GET /accounts/\{account-id\}/groups/ (List Groups)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Lists all groups that contain the specified user as a member.
+
+.Request
+----
+  GET /a/accounts/self/groups/ HTTP/1.0
+----
+
+As result a list of link:rest-api-groups.html#group-info[GroupInfo]
+entries is returned.
+
+.Response
+----
+  HTTP/1.1 200 OK
+  Content-Disposition: attachment
+  Content-Type: application/json;charset=UTF-8
+
+  )]}'
+  [
+    {
+      "kind": "gerritcodereview#group",
+      "id": "global%3AAnonymous-Users",
+      "url": "#/admin/groups/uuid-global%3AAnonymous-Users",
+      "options": {
+      },
+      "description": "Any user, signed-in or not",
+      "group_id": 2,
+      "owner_id": "6a1e70e1a88782771a91808c8af9bbb7a9871389"
+    },
+    {
+      "kind": "gerritcodereview#group",
+      "id": "834ec36dd5e0ed21a2ff5d7e2255da082d63bbd7",
+      "url": "#/admin/groups/uuid-834ec36dd5e0ed21a2ff5d7e2255da082d63bbd7",
+      "options": {
+        "visible_to_all": true,
+      },
+      "group_id": 6,
+      "owner_id": "834ec36dd5e0ed21a2ff5d7e2255da082d63bbd7"
+    },
+    {
+      "kind": "gerritcodereview#group",
+      "id": "global%3ARegistered-Users",
+      "url": "#/admin/groups/uuid-global%3ARegistered-Users",
+      "options": {
+      },
+      "description": "Any signed-in user",
+      "group_id": 3,
+      "owner_id": "6a1e70e1a88782771a91808c8af9bbb7a9871389"
+    }
+  ]
+----
+
+.List all groups that contain you as a member
+****
+get::/accounts/self/groups/
+****
+
 [[get-avatar]]
 GET /accounts/\{account-id\}/avatar (Get Avatar)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~