Token Manager: update documentation.

Token manager unregisters a token when you get the stored interface.

Test: pass
Change-Id: Id3560d90a6009b48c3333fb8a6831a334173d022
diff --git a/transport/token/1.0/ITokenManager.hal b/transport/token/1.0/ITokenManager.hal
index dc4134a..2f0650b 100644
--- a/transport/token/1.0/ITokenManager.hal
+++ b/transport/token/1.0/ITokenManager.hal
@@ -43,7 +43,8 @@
     unregister(uint64_t token) generates (bool success);
 
     /**
-     * Fetches an interface from a provided token.
+     * Fetches an interface from a provided token. This must also unregister the
+     * token.
      *
      * @param token Token recieved from createToken
      * @return store Interface registered with createToken and the corresponding