`.gitignore` could use negative patterns

[toslunar]

Even if we want to ensure that there's no tracked-but-ignored file, I suggest

-docs/source/_static/embed-bundle.js
-docs/source/_static/embed-bundle.js.map
+docs/source/_static/*
+!docs/source/_static/helper.js

and

-{{ cookiecutter.python_package_name  }}/nbextension/index.*
+{{ cookiecutter.python_package_name  }}nbextension/*
+!{{ cookiecutter.python_package_name  }}/nbextension/extension.js

In my project, in the directories there are generated files

• index.js.LICENSE.txt
• image files (after I added file-loader to webpack.config.js rules)