add forbid-submodules hook

README.md

diff --git a/README.md b/README.md
index 411529a..1026d3f 100644
--- a/README.md
+++ b/README.md
@@ -133,6 +133,12 @@
 #### `forbid-new-submodules`
 Prevent addition of new git submodules.
 
+This is intended as a helper to migrate away from submodules.  If you want to
+ban them entirely use `forbid-submodules`
+
+#### `forbid-submodules`
+forbids any submodules in the repository.
+
 #### `mixed-line-ending`
 Replaces or checks mixed line ending.
   - `--fix={auto,crlf,lf,no}`