fix: update README

Signed-off-by: Frost Ming <me@frostming.com>

README.md

@@ -15,7 +15,7 @@ Include the action in your workflow yaml:
 steps:
  - uses: actions/checkout@v3
  - name: Setup PDM
- uses: pdm-project/setup-pdm@v3
+ uses: pdm-project/setup-pdm@v4
  # You are now able to use PDM in your workflow
  - name: Install dependencies
  run: pdm install
@@ -30,6 +30,7 @@ This action supports the following inputs:
 | Input | Default | Description |
 | -------------------------- | --------------------- | ------------------------------------------------------------------------------------------------------------------------------------ |
 | `python-version` | `3.x` | Version range or exact version of a Python version to use, using SemVer's version range syntax. |
+| `python-version-file` | `.python-version` | File containing the Python version to use. Example: .`python-version` |
 | `architecture` | `x64` | The target architecture (x86, x64) of the Python interpreter. |
 | `allow-python-prereleases` | `false` | Allow prerelease versions of Python to be installed. |
 | `token` | `${{ github.token }}` | Used to pull python distributions from actions/python-versions. Since there's a default, this is typically not supplied by the user. |