Add return value example to ssh key creation

Signed-off-by: Loic Dachary <loic@dachary.org>

doc/api/users.md

@@ -322,6 +322,15 @@ Parameters:
 - `title` (required) - new SSH Key's title
 - `key` (required)   - new SSH key
 
+```json
+{
+  "created_at": "2015-01-21T17:44:33.512Z",
+  "key": "ssh-dss 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 loic@call",
+  "title": "ABC",
+  "id": 4
+}
+```
+
 ## Add SSH key for user
 
 Create new key owned by specified user. Available only for admin