Docs: simplier set up for GitHub actions

[IvanGoncharov]

Currently, docs suggest this setup

name: Lint GitHub Actions workflows
on: [push, pull_request]

jobs:
  actionlint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Download actionlint
        id: get_actionlint
        run: bash <(curl https://raw.githubusercontent.com/rhysd/actionlint/main/scripts/download-actionlint.bash)
        shell: bash
      - name: Check workflow files
        run: ${{ steps.get_actionlint.outputs.executable }} -color
        shell: bash

But I found you can do it way simpler with 2 steps instead of 3 and with caching:

name: Lint GitHub Actions workflows
on: [push, pull_request]

jobs:
  actionlint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Check workflow files
        uses: docker://rhysd/actionlint:latest
        with:
          args: -color

[rhysd]

That would be also good way to use actionlint on CI though preparing Docker image would takes a bit longer. I'll add it to document.