feat: add lint workflow (#648)

.github/workflows/lint.yml

+name: lint
+
+on: [push, pull_request]
+
+jobs:
+  lint:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Python 3.8
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.8
+      - name: Install pre-commit hook
+        run: |
+          python -m pip install pre-commit
+          pre-commit install
+      - name: Linting
+        run: pre-commit run --all-files