Adding a config for a CI action

.github/workflows/main.yml

+name: CI
+on: [push]
+
+jobs:
+  build:
+    name: ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macOS-latest]
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: Compile
+      run: make
+    - name: Test
+      run: make test