add github actions

.github/workflows/esp32_build.yml

@@ -0,0 +1,24 @@
+name: ESP32 Build
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v1
+
+      - name: Install PlatformIO
+        run: |
+          python -m pip install --upgrade pip
+          pip install -U platformio
+          platformio update
+
+      - name: Build bare metal
+        run: platformio run