fix docs and spec

spec/api-protocol-spec.js

@@ -841,6 +841,12 @@ describe('protocol module', function () {
       })
     })
 
+    it('throws when called after ready event', function () {
+      assert.throws(function () {
+        protocol.registerStandardSchemes(['some-scheme'])
+      }, 'protocol.registerStandardSchemes should be called before app is ready')
+    })
+
     it('resolves relative resources', function (done) {
       var handler = function (request, callback) {
         if (request.url === imageURL) {