General Improvements (#70)

# General Improvements

> This is a classic @GrantBirki drive-by PR 🚗

This pull request does the following:

- Lightly updates and formats a few existing Actions workflows
- Adds a new `package-check` workflow to validate the contents of the
`dist/` directory have been properly built
- Uses a `.node-version` file so that local development and Actions
remain on the same pinned version of node
- Adds status badges to the readme for visual effect ⭐ 🎨

package.json

@@ -5,7 +5,7 @@
   "version": "1.5.1",
   "description": "GitHub Action for creating a GitHub App Installation Access Token",
   "scripts": {
-    "build": "esbuild main.js post.js --bundle --outdir=dist --out-extension:.js=.cjs --platform=node --target=node16.16",
+    "build": "esbuild main.js post.js --bundle --outdir=dist --out-extension:.js=.cjs --platform=node --target=node20.0.0",
     "test": "c8 --100 ava tests/index.js",
     "coverage": "c8 report --reporter html",
     "postcoverage": "open-cli coverage/index.html"