chore(api-builder): add ngModule dgeni tag

tools/api-builder/angular.io-package/tag-defs/index.js

@@ -9,4 +9,5 @@ module.exports = [
   require('./experimental'),
   require('./docsNotRequired'),
   require('./security'),
+  require('./ngModule'),
 ];

tools/api-builder/angular.io-package/tag-defs/ngModule.js

@@ -0,0 +1,6 @@
+module.exports = function() {
+  return {
+    name: 'ngModule',
+    multi: true
+  };
+};