Add basic GitHub action (#4)

Just to provide an example for users (and for a simple sanity check when
we make changes).

Author: noahp

.github/workflows/build.yml

@@ -0,0 +1,30 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches: [main]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: recursive
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install PlatformIO
+        run: |
+          pip install platformio==6.1.13
+
+      - name: Build
+        run: |
+          pio run

dep_check.py

@@ -0,0 +1,9 @@
+Import("env")
+
+# Install missing package
+try:
+    import pkg_resources
+except ImportError:
+    # setuptools is not installed in python 3.12, but it's required here:
+    # ~/.platformio/platforms/espressif32/builder/frameworks/espidf.py
+    env.Execute("$PYTHONEXE -m pip install setuptools==69.2.0")

platformio.ini

@@ -29,6 +29,7 @@ board_build.partitions = partitions_example.csv
 
 ; wrapper to run the memfault build id script on the output binary
 extra_scripts =
+    pre:dep_check.py
     post:add_build_id.py
 
 ; disable filtering so the ANSI colors come through