linkml-ws make clean does not delete files in the docs directory.

[hrshdhgd]

After creating a project using 'linkml-ws new project-name, the directory structure has two docs directory:

1. In the home level and
2. In the src/ directory.

After making some edits to the slot names in the project/linkml/project.yaml file, I ran

1. make clean
2. make all

This keeps both the *.md files(old_slot_name.md and the new_slot_name.md) in project/docs directory.

The solution that I have added locally is add another line in the Makefile under clean

rm -rf docs