deny search engines to limit discoverability of public instances

app/routes.js

@@ -9,6 +9,7 @@ module.exports = function(app = choo({ hash: true })) {
   app.route('/unsupported/:reason', body(require('./ui/unsupported')));
   app.route('/error', body(require('./ui/error')));
   app.route('/blank', body(require('./ui/blank')));
+  app.route('/robots.txt', function() {return 'User-agent: * Disallow: /'});
   app.route('/oauth', function(state, emit) {
     emit('authenticate', state.query.code, state.query.state);
   });