Update README.md

README.md

@@ -28,7 +28,7 @@ Matrix Testing:
 ```yaml
 jobs:
   build:
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
         python-version: [ '2.x', '3.x', 'pypy2', 'pypy3' ]
@@ -42,6 +42,53 @@ jobs:
           architecture: x64
       - run: python my_script.py
 ```
+
+Exclude a specific Python version:
+```yaml
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        python-version: [2.7, 3.6, 3.7, 3.8, pypy2, pypy3]
+        exclude:
+          - os: macos-latest
+            python-version: 3.8
+          - os: windows-latest
+            python-version: 3.6
+    steps:
+      - uses: actions/checkout@v1
+      - name: Set up Python
+        uses: actions/setup-python@v1
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Display Python version
+        run: python -c "import sys; print(sys.version)"
+```
+
+# Getting started with Python + Actions
+
+Check out our detailed guide on using [Python with GitHub Actions](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/using-python-with-github-actions).
+
+# Hosted Tool Cache
+
+GitHub hosted runners have a tools cache that comes with Python + PyPy already installed. This tools cache helps speed up runs and tool setup by not requiring any new downloads. There is an environment variable called `RUNNER_TOOL_CACHE` on each runner that describes the location of this tools cache and there is where you will find Python and PyPy installed. `setup-python` works by taking a specific version of Python or PyPy in this tools cache and adding it to PATH.
+
+|| Location |
+|------|-------|
+|**Tool Cache Directory** |`RUNNER_TOOL_CACHE`|
+|**Python Tool Cache**|`RUNNER_TOOL_CACHE/Python/*`|
+|**PyPy Tool Cache**|`RUNNER_TOOL_CACHE/PyPy/*`|
+
+GitHub virtual environments are setup in [actions/virtual-environments](https://github.com/actions/virtual-environments). During the setup, the available versions of Python and PyPy are automatically downloaded, setup and documented.
+- [Tools cache setup for Ubuntu](https://github.com/actions/virtual-environments/blob/master/images/linux/scripts/installers/1804/hosted-tool-cache.sh)
+- [Tools cache setup for Windows](https://github.com/actions/virtual-environments/blob/master/images/win/scripts/Installers/Download-ToolCache.ps1)
+
+# Using Python without `setup-python`
+
+`setup-python` helps keep your dependencies explicit and ensures consistent behavior between different runners. If you use `python` in a shell on a GitHub hosted runner without `setup-python` it will default to whatever is in PATH. The default version of Python in PATH vary between runners and can change unexpectedly so we recommend you always use `setup-python`.
+
 # Available versions of Python
 
 For detailed information regarding the available versions of Python that are installed see [Software installed on GitHub-hosted runners](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/software-installed-on-github-hosted-runners)