[11.x] Adds documentation for pint --diff=[DIFF] (#10100)

* adds documentation for pint --diff

* Update pint.md

---------

Co-authored-by: Taylor Otwell <[email protected]>

Author: ProjektGopher

pint.md

@@ -55,6 +55,12 @@ If you would like Pint to simply inspect your code for style errors without actu
 ./vendor/bin/pint --test
 ```
 
+If you would like Pint to only modify the files that differ from the provided branch according to Git, you may use the `--diff=[branch]` option. This can be effectively used in your CI environment (like GitHub actions) to save time by only inspecting new or modified files:
+
+```shell
+./vendor/bin/pint --diff=main
+```
+
 If you would like Pint to only modify the files that have uncommitted changes according to Git, you may use the `--dirty` option:
 
 ```shell