chore(github): add build workflow for test builds

Signed-off-by: Stefan Dej <meteyou@gmail.com>

.github/workflows/build.yml

@@ -0,0 +1,34 @@
+name: Build Mainsail
+on:
+  push:
+    branches:
+      - develop
+  pull_request:
+    branches:
+      - develop
+jobs:
+  build-mainsail:
+    name: Build mainsail.zip
+    runs-on: ubuntu-latest
+    steps:
+      - name: Fetch repo
+        uses: actions/checkout@v2
+
+      - name: Install node
+        uses: actions/setup-node@v2
+        with:
+          node-version: '16'
+
+      - name: Install dependencies
+        run: npm install
+
+      - name: Build
+        run: npm run build
+
+      - name: Copy output
+        run: cp ${{ github.workspace }}/dist/mainsail.zip mainsail-latest.zip
+
+      - uses: actions/upload-artifact@v1
+        with:
+          name: mainsail-latest.zip
+          path: mainsail-latest.zip