Added GitHub Actions workflow to publish release on PYPI:

- Added workflow
- Updated CONTRIBUTING.md page

.github/workflows/release.yml

@@ -0,0 +1,28 @@
+name: Build distribution
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.6","3.7"]
+    steps:
+      - name: Checkout source
+        uses: actions/checkout@v2
+      - name: Set up Python ${{ matrix.python-version }}
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install build dependencies
+        run: python -m pip install build wheel
+      - name: Build distributions
+        shell: bash -l {0}
+        run: python setup.py sdist bdist_wheel
+      - name: Publish package to PYPI
+        if: github.repository == 'abatomunkuev/static_site_generator' && github.event_name == 'push' && startsWith(github.ref, 'refs/tags')
+        uses: pypa/gh-action-pypi-publish@master
+        with:
+          passwords: ${{secrets.pypi_password}}

CONTRIBUTING.md

@@ -43,4 +43,23 @@ pytest tests/
 You can run all the tests and code-formatting in one-step by running:
 ```
 ./run_python_tests.sh
+```
+
+## Releasing
+Releases are published automatically when a tag is pushed to GitHub.
+```bash
+    # Set next version number
+   export RELEASE=x.x.x
+
+   # Create tags
+   git commit --allow-empty -m "Release $RELEASE"
+   git tag -a $RELEASE -m "Version $RELEASE"
+
+   # Push
+   git push upstream --tags
+```
+
+Pushing upstream assumes we are working from a fork, if we are not doing that that it would be:
+```bash
+    git push origin --tags
 ```