Add setup-node code to examples

We are calling it out that this action does not setup node and we have to explicitly do it, but sometimes it is not obviously enough to read through the examples till the end and find out about the warning. Instead we can add setup-node code in the README examples itself so that it becomes absolutely apparent.
Something like below:

on:
  - push
  - pull_request

jobs:
  install:
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v2
      - name: Use Node.js 12
        uses: actions/setup-node@v2
        with:
          node-version: 12

      - uses: pnpm/action-setup@v2.1.0
        with:
          version: 6.0.2
          run_install: |
            - recursive: true
              args: [--frozen-lockfile, --strict-peer-dependencies]
            - args: [--global, gulp, prettier, typescript]

If this is okay, will raise a PR for the same.

Review the README examples and the existing warning about Node.js setup. Add the setup-node step to the relevant examples so the requirement is visible within each example, then verify that the examples remain valid GitHub Actions YAML.