docs: document mutations params argument (#259)

Co-authored-by: michael-small <33669563+michael-small@users.noreply.github.com>

Author: freon27

docs/docs/mutations.md

@@ -143,7 +143,12 @@ httpMutation({
 
 ### Callbacks
 
-In the mutation: _optional_ `onSuccess` and `onError` callbacks
+In the mutation: _optional_ `onSuccess` and `onError` callbacks.
+
+The callbacks are called with two parameters:
+
+1. The result of the mutation (`onSuccess`) or the error (`onError`)
+2. The parameter passed when calling the mutation
 
 ```ts
 ({
@@ -159,6 +164,14 @@ In the mutation: _optional_ `onSuccess` and `onError` callbacks
     console.error('Error occurred:', error);
   },
 });
+
+// using the passed parameter
+({
+  onSuccess: (_result, params) => {
+    // after successful deletion
+    store.listResource.set(store.listResource.value().filter((item) => item.id !== params.id));
+  },
+});
 ```
 
 ### Flattening operators