fix(ci): add markdownlint

.gitea/workflows/markdown-linters.yaml

@@ -0,0 +1,26 @@
+name: 'Lint Markdown files'
+
+on:
+  pull_request:
+    types:
+    - opened
+    - reopened
+    - synchronize
+  push:
+    branches:
+    - master
+  workflow_dispatch: {}
+
+jobs:
+  markdown-lint:
+    runs-on:
+    - ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4.2.2
+    - run: |
+        docker run \
+          --rm \
+          --volume $(pwd):$(pwd) \
+          --workdir $(pwd) \
+            git.cryptic.systems/volker.raschek/markdownlint:0.44.0 \
+              .