Document login API

src/RtsClient.js

@@ -78,6 +78,13 @@ export default class RtsClient {
         );
     }
 
+    /**
+     * Signal to the RTS that a login has occurred and that a user requires their team's
+     * token.
+     * @param {string} userId the user ID of the user who is a member of a team.
+     * @returns {Promise} a promise that resolves to { team_token: 'sometoken' } upon
+     * success.
+     */
     login(userId) {
         return request(this._url + '/login',
             {