Add drift correction docs

docs/ref-gitrepo.md

@@ -109,4 +109,13 @@ spec:
   # If empty, the "default" cluster group is used.
   #
   # targets: ...
+  #
+  # Drift correction removes any external change made to resources managed by Fleet. It performs a helm rollback, which uses
+  # a three-way merge strategy by default. It will try to update all resources by doing a PUT request if force is enabled.
+  # Failed rollback will be removed from the helm history unless keepFailHistory is set to true.
+  #
+  #  correctDrift:
+  #    enabled: false
+  #    force: false #Warning: it might recreate resources if set to true
+  #    keepFailHistory: false
 ```