Add a workflow to generate folder images

This workflow will generate a bunch of images and place them on a branch called
"folder-images", which (once enabled via github pages) will appear on
adafruit.github.io.

The workflow is triggered:
 * on commits to the main branch, including merged pull requests
 * daily, after the bundle is updated
 * on request via the github web page

Typically, this means that the images will be available (well) within an hour
after a pull request is merged, and will be updated daily if required by
changes to the requirements of libraries.

Author: jepler

.github/workflows/images.yml

@@ -0,0 +1,52 @@
+name: Generate folder images
+
+on:
+  schedule:
+    - cron: '0 10 * * *'
+  workflow_dispatch:
+  push:
+    branches: [master]
+
+concurrency:
+  group: folder-images
+  cancel-in-progress: true
+
+jobs:
+  update-images:
+    runs-on: ubuntu-20.04
+    steps:
+    - name: Dump GitHub context
+      env:
+        GITHUB_CONTEXT: ${{ toJson(github) }}
+      run: echo "$GITHUB_CONTEXT"
+
+    - uses: actions/checkout@v2.2.0
+
+    - name: Set up Python 3.9
+      uses: actions/setup-python@v1
+      with:
+        python-version: 3.9
+
+    - name: Checkout screenshot maker
+      run: git clone --depth=1 https://github.com/circuitpython/CircuitPython_Library_Screenshot_Maker
+
+    - name: Install dependencies
+      run: pip install -r CircuitPython_Library_Screenshot_Maker/requirements.txt
+
+    - name: Generate images
+      run: |
+        cd CircuitPython_Library_Screenshot_Maker
+        env LEARN_GUIDE_REPO=../ python3 ./create_requirement_images.py
+
+    - name: Commit updates
+      run: |
+        cd CircuitPython_Library_Screenshot_Maker/generated_images
+        git config --global user.name "${GITHUB_ACTOR} (github actions cron)"
+        git config --global user.email "${GITHUB_ACTOR}@users.noreply.github.com"
+        git config --global init.defaultBranch main
+        git init
+        for i in *.png; do echo "<a href=\"$i\">$i</a><br>"; done > index.html
+        git add *.png index.html
+        git remote add origin https://${GITHUB_ACTOR}:${{ secrets.GITHUB_TOKEN }}@github.com/${{ github.repository }}
+        if git commit -m"update images"; then git push -f origin HEAD:folder-images; fi
+