resolved comments, update readme, add e2e tests.

.github/workflows/test-pypy.yml

@@ -0,0 +1,47 @@
+name: Validate PyPy e2e
+on: 
+  push:
+    branches:
+      - main
+    paths-ignore:
+      - '**.md'
+  pull_request:
+    paths-ignore:
+      - '**.md'
+  schedule:
+    - cron: 0 0 * * *
+
+jobs:
+  setup-pypy:
+    name: Setup PyPy ${{ matrix.pypy }} ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [macos-latest, windows-latest, ubuntu-18.04, ubuntu-20.04]
+        pypy:
+        - 'pypy-2.7'
+        - 'pypy-3.6'
+        - 'pypy-3.7'
+        - 'pypy-2.7-v7.3.2'
+        - 'pypy-3.6-v7.3.2'
+        - 'pypy-3.7-v7.3.2'
+        - 'pypy-3.6-v7.3.x'
+        - 'pypy-3.7-v7.x'
+        - 'pypy-3.6-v7.3.3rc1'
+        - 'pypy-3.7-nightly'
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+  
+      - name: setup-python ${{ matrix.pypy }}
+        uses: ./
+        with:
+          python-version: ${{ matrix.pypy }}
+  
+      - name: PyPy and Python version
+        run: python --version
+  
+      - name: Run simple code
+        run: python -c 'import math; print(math.factorial(5))'