Check Front Matter

[szepeviktor]

        -
            name: "Remove document contents"
            run: |
                git ls-files --cached -z -- 'docs/**.md' \
                   | xargs --null --max-args=1 -- sed -i -e 'N;P;/---\n$/Q;D'
        -
            name: "Check Front Matter"
            run: |
                git ls-files --cached -z -- 'docs/**.md' \
                   | xargs --null --max-args=1 -- python -m yamllint --strict