Create build.yml

quite a cool auto-build if I might say.  Will make it recover /dist shortly.

.github/workflows/build.yml

@@ -0,0 +1,40 @@
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os:
+          - ubuntu-latest
+          - macos-latest
+          - windows-latest
+        node_version:
+          - 10
+          - 12
+          - 14
+          - 15
+        architecture:
+          - x64
+          - arm64
+        # an extra windows-x86 run:
+#        include:
+#          - os: windows-latest
+#            node_version: 15
+#            architecture: arm64
+#          - os: macos-latest
+#            node_version: 15
+#            architecture: arm64
+    name: Node ${{ matrix.node_version }} - ${{ matrix.architecture }} on ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v2
+      - name: Setup node
+        uses: actions/setup-node@v2
+        with:
+          node-version: ${{ matrix.node_version }}
+          architecture: ${{ matrix.architecture }}
+      - run: npm install
+      - run: npm test
+      - run: npm run build
+      - uses: actions/upload-artifact@v2
+        with:
+          name: executable
+          path: dist/