Easy content changes to relay mutation docs
Summary:
* Add documentation about second parameter to upater in various places
* Add recommendation that the like_count is read out in advance
@@ -84,7 +84,7 @@ environment.commitPayload(operation, payload);
```
* An `OperationDescriptor` can be created by `createOperationDescriptor`; it takes the query and the query variables.
-* The payload can be typed using the Flow type generated by adding `@raw_response_type` to the query.
+* The payload can be typed using the Flow type generated by adding the directive `@raw_response_type` to the query.
* Note that any local data updates will automatically cause components subscribed to the data to be notified of the change and re-render.
<FbLocalDataUpdatesFlow />
