Add Github CI

.github/workflows/build.yml

@@ -0,0 +1,25 @@
+name: Build Firmware
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: "recursive"
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.9"
+      - name: Install dependencies
+        run: |
+          pip install -U https://github.com/platformio/platformio/archive/develop.zip
+      - name: Build firmware
+        run: |
+          pio run