Update doc for request handler

bramble-core/src/main/java/org/briarproject/bramble/mailbox/protocol/MailboxRequestHandler.java

@@ -11,6 +11,7 @@ public interface MailboxRequestHandler {
 	 * @param request
 	 * @throws ProtocolException If this function throws a Protocol exception,
 	 * an error response will be sent
+	 * NOTE: Ensure that the ProtocolException does not include sensitive information
 	 */
 	void handleRequest(MailboxRequest request) throws ProtocolException;