Add GitHub Actions for testing matchers

.github/workflows/main.yml

@@ -0,0 +1,13 @@
+name: Main CI
+on: [push]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: Setup local Android problem matchers
+      run: |
+        ./index.js
+    - name: Print example problems
+      run: |
+        ./test.js