Put back GitHub workflow

.github/workflows/luacheck.yml

@@ -0,0 +1,21 @@
+name: Luacheck
+
+on: [push, pull_request]
+
+jobs:
+
+  luacheck:
+    runs-on: ubuntu-20.04
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v2
+    - name: Setup ‘lua’
+      uses: leafo/gh-actions-lua@v8
+      with:
+        luaVersion: 5.1
+    - name: Setup ‘luarocks’
+      uses: leafo/gh-actions-luarocks@v4
+    - name: Setup ‘luacheck’
+      run: luarocks install luacheck
+    - name: Run ‘luacheck’ linter
+      run: lua luacheck.lua .