fix typos in docstring

operations/ensure_prepend.py

@@ -6,7 +6,7 @@ Filter to modify `setenv` statements in modulefiles to `prepend-path` statements
 Usage:
     tools/ensure_prepend.py PATH MANPATH PYTHONPATH <../build.52.VGk/test.mod
 or
-    module sh-to-module bash somescript.sh | tools/ensure_prepend.py PATH MANPATH PYTHONPATH > path/to/module
+    module sh-to-mod bash somescript.sh | ensure_prepend.py PATH MANPATH PYTHONPATH > path/to/module
 """
 
 import logging