added pio build

.forgejo/workflows/demo.yaml

@@ -1,6 +1,21 @@
 on: [push]
 jobs:
-  test:
+  build:
     runs-on: ubuntu-latest
+
     steps:
-      - run: echo All Good
+      - uses: actions/checkout@v4
+      - uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cache/pip
+            ~/.platformio/.cache
+          key: ${{ runner.os }}-pio
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+      - name: Install PlatformIO Core
+        run: pip install --upgrade platformio
+
+      - name: Build PlatformIO Project
+        run: pio run