Update lefthook.yml to automatically add generated signatures to git staging

Author: Syati

lefthook.yml

@@ -1,7 +1,7 @@
 prepare-commit-msg:
   commands:
     rbs-inline:
-      run: bundle exec rbs-inline --output=sig lib/**/*.rb
+      run: bundle exec rbs-inline --output=sig lib/**/*.rb && git add sig/
 
 pre-commit:
   commands: