Run `awesome-lint` on new additions (#1962)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

.github/workflows/main.yml

@@ -0,0 +1,14 @@
+on:
+  pull_request:
+    branches: [main]
+    paths:
+      - 'readme.md'
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - name: awesome-lint
+        run: ./.github/workflows/repo_linter.sh

.github/workflows/repo_linter.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+
+# Find the repo in the git diff and then set it to an env variables.
+REPO_TO_LINT=$(
+	git diff main readme.md |
+	# Look for changes (indicated by lines starting with +).
+	grep ^+ |
+	# Get the line that includes the readme.
+	grep -Eo 'https.*#readme' |
+	# Get just the URL.
+	sed 's/#readme//')
+
+# If there's no repo found, exit quietly.
+if [ -z ${REPO_TO_LINT+x} ]; then
+	echo "No new link found in the format:  https://....#readme"
+else
+	echo "Cloning $REPO_TO_LINT"
+	mkdir cloned
+	cd cloned
+	git clone --depth=1 "$REPO_TO_LINT" .
+	npx awesome-lint
+fi