Change the lua length operator to do the obvious thing.

build.py

@@ -379,6 +379,10 @@ def generate_integration_code_workspace():
 def build_clean():
     """
     This code is underdeveloped.
+
+    For a more aggressive form of cleaning, use 'git clean -xfd',
+    which resets your git repository to its pristine state.
+    DANGER: this deletes any new source code you've created!
     """
     shell(f"{INTEGRATION}/luprex", "make clean")
     shell(INTEGRATION, f"{UNREALENGINE}/Engine/Build/BatchFiles/{BUILD_BAT} -waitmutex IntegrationEditor {OS} {DEBUG} {INTEGRATION}/Integration.uproject -clean")