tools/docker: add README.md file to be displayed on Docker Hub

Closes https://github.com/espressif/esp-idf/issues/7933

.github/workflows/docker.yml

@@ -73,3 +73,15 @@ jobs:
           build-args: |
             IDF_CLONE_URL=${{ github.server_url }}/${{ github.repository }}.git
             IDF_CLONE_BRANCH_OR_TAG=${{ env.CLONE_BRANCH_OR_TAG }}
+
+      - name: Update Docker Hub repository description (master branch)
+        if: ${{ github.ref_type == 'branch' && github.ref_name == 'master' }}
+        uses: peter-evans/dockerhub-description@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          # Token based authentication is not supported here:
+          # https://github.com/peter-evans/dockerhub-description/issues/10
+          # https://github.com/docker/roadmap/issues/115#issuecomment-891694974
+          password: ${{ secrets.DOCKERHUB_PASSWORD }}
+          repository: ${{ env.DOCKERHUB_REPO }}
+          readme-filepath: ./tools/docker/README.md