add gitea action

.gitea/workflows/build.yml

@@ -0,0 +1,15 @@
+name: mkdocs build
+
+on:
+  push:
+    branches:
+      - "main"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Build with MkDocs
+        uses: romw314/mkdocs-action@v2 # https://github.com/marketplace/actions/mkdocs-build