docs(injector): add docs for $injector.has

src/auto/injector.js

@@ -151,6 +151,18 @@ function annotate(fn) {
  * @returns {*} the value returned by the invoked `fn` function.
  */
 
+/**
+ * @ngdoc method
+ * @name AUTO.$injector#has
+ * @methodOf AUTO.$injector
+ *
+ * @description
+ * Allows the user to query if the particular service exist.
+ *
+ * @param {string} Name of the service to query.
+ * @returns {boolean} returns true if injector has given service.
+ */
+
 /**
  * @ngdoc method
  * @name AUTO.$injector#instantiate