[Feature] Support 'python -m mim' usage (#158)

* feat(mim): support 'python -m mim' usage

* feat(mim): add test mim cli test

* move mim cli test to build.yml

.github/workflows/build.yml

@@ -68,7 +68,10 @@ jobs:
       - name: Build and install
         run: rm -rf .eggs && python -m pip install -e .
       - name: Validate the installation
-        run: python -c "import mim"
+        run: |
+          python -c "import mim"
+          mim --help
+          python -m mim --help
       - name: Install unittest dependencies
         run: python -m pip install -r requirements/tests.txt
       - name: Run unittests and generate coverage report

mim/__main__.py

@@ -0,0 +1,6 @@
+# Copyright (c) OpenMMLab. All rights reserved.
+"""With this module, we can use `python -m mim`."""
+from .cli import cli
+
+if __name__ == '__main__':
+    cli()