documenting identity keys

Author: justinbmeyer

doc/prototype/identity-keys.md

@@ -1,2 +1,21 @@
 @function can-query-logic.prototype.identityKeys identityKeys
 @parent can-query-logic.prototype
+
+
+@description Return the identity keys.
+
+@signature `queryLogic.identityKeys()`
+
+Return the identity keys used to identity instances associated with the query logic:
+
+```js
+import QueryLogic from "can-query-logic";
+
+var queryLogic = new QueryLogic({
+    identity: ["_id"]
+});
+
+queryLogic.identityKeys() //-> ["_id"]
+```
+
+@return {Array<String>} An Array of the identity keys.