Update Docker Hub README and keep it in sync with this repository.

This commit
* adds a new docs page (`dockerhub.md`) that contains Docker Hub README
* updates the default config that gets backed into the docker image
* updates CI with a new workflow job that keeps Docker Hub README in
  sync with the contents of the `docs/dockerhub.md` file

Co-authored-by: CrazyMax <github@crazymax.dev>
Signed-off-by: Milos Gajdos <milosthegajdos@gmail.com>

.github/dockerhub-readme.yml

@@ -0,0 +1,32 @@
+name: dockerhub-readme
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+on:
+  push:
+    branches:
+      - 'main'
+    paths:
+      - '.github/dockerhub-readme.yml'
+      - 'docs/dockerhub.md'
+
+env:
+  DOCKERHUB_SLUG: distribution/distribution
+
+permissions:
+  contents: read
+
+jobs:
+  update:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Update Docker Hub README
+        uses: peter-evans/dockerhub-description@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+          repository: ${{ env.DOCKERHUB_SLUG }}
+          readme-filepath: ./docs/dockerhub.md