Add simple gitea runner demo

.gitea/workflows/main.yml

@@ -0,0 +1,20 @@
+name: CI checks
+run-name: CI checks that run when main branch is changed
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  fmt:
+    runs-on: ubuntu-latest
+    name: ubuntu / stable / fmt
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install stable
+        uses: https://github.com/dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt
+      - name: cargo fmt --check
+        run: cargo fmt --check --all