Update API docs on ID character restrictions

docs/api.json

@@ -9,7 +9,7 @@
         "name": "id",
         "optional": true,
         "type": "string",
-        "description": "Other peers can connect to this peer using the provided ID. If no ID is given, one will be generated by the brokering server.<span class='warn'>It's not recommended that you use this ID to identify peers, as it's meant to be used for brokering connections only. You're recommended to set the <a href='#peerconnect-options'><code>metadata</code></a> option to send other identifying information.</span>"
+        "description": "Other peers can connect to this peer using the provided ID. If no ID is given, one will be generated by the brokering server. The ID must start and end with a lower or upper case charcter or a digit. In the middle of the ID spaces, dashes (-) and underscores (_) are allowed.<span class='warn'>It's not recommended that you use this ID to identify peers, as it's meant to be used for brokering connections only. You're recommended to set the <a href='#peerconnect-options'><code>metadata</code></a> option to send other identifying information.</span>"
       },
       {
         "name": "options",