doc(readme): add workflow example which caches the virtual environment

README.md

@@ -46,6 +46,62 @@ jobs:
         run: poetry --help
 ```
 
+### Workflow example: cache the virtual environment
+
+It is possible to combine `actions/poetry` with [actions/cache](https://github.com/actions/cache) to speed up the installation of dependencies.
+The recipe is:
+
+1. to ask `poetry` to create a virtual environment inside the project:
+it creates a local `.venv/` folder that can be cached
+2. to create a cache key that involves the contents of the `poetry.lock` file:
+if the contents change (meaning that dependencies have changed), then the cache needs to be invalidated and recreated
+
+For the 1st step, you either need:
+
+- to have a `poetry.toml` file at the root of your project with these 2 settings:
+
+```ini
+[virtualenvs]
+create = true
+in-project = true
+```
+
+- or to run the following commands in the github actions to create the `poetry.toml` file:
+
+```sh
+poetry config virtualenvs.create true --local
+poetry config virtualenvs.in-project true --local
+```
+
+Here is an example of how the steps must be declared:
+
+```yaml
+jobs:
+  ci:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Python
+        uses: actions/setup-python@v4
+        # see details (matrix, python-version, python-version-file, etc.)
+        # https://github.com/actions/setup-python
+      - name: Install poetry
+        uses: abatilo/actions-poetry@v2
+      - name: Setup a local virtual environment (if no poetry.toml file)
+        run: |
+          poetry config virtualenvs.create true --local
+          poetry config virtualenvs.in-project true --local
+      - uses: actions/cache@v3
+        name: Define a cache for the virtual environment based on the dependencies lock file
+        with:
+          path: ./.venv
+          key: venv-${{ hashFiles('poetry.lock') }}
+      - name: Install the project dependencies
+        run: poetry install
+      - name: Run the automated tests (for example)
+        run: poetry run pytest -v
+```
+
 ## License
 
 [MIT License - abatilo/actions-poetry]