update readme to reflect boolean as one of the options on invalidate

Author: thiagonzalez

README.md

@@ -330,6 +330,15 @@ const [mutation] = useMutation(['todos', 1], {
 })
 ```
 
+To ignore invalidation, even with the same type as your mutation, just set `false` for the `invalidate` option:
+```JavaScript
+const [mutation] = useMutation(['todos', 1], {
+  invalidate: false
+})
+```
+
+This way the list of "todos" won't be updated after a mutation.
+
 ## Manual Requests
 Manual API requests can be performed through the client instance, which can be obtained with the [useClient](#useClient) hook