Convert ocitools from Docbook to CommonMark

[ryantm]

This issue tracks the conversion of /doc/builders/images/ocitools.xml from Docbook to CommonMark per RFC 72.

If you intend to work on this conversion, please comment below!

Conversion instructions

1. Comment here that you intend to work on it. (Please also post if you stop working on it.)
2. Checkout a new branch of nixpkgs master.
3. Edit doc/builders/images.xml: change ocitools.xml to ocitools.section.xml.
4. Rename doc/builders/images/ocitools.xml to ocitools.section.md.
5. Convert the contents from Docbook to CommonMark. Follow conversion best practices. Use existing .md sections for inspiration.
6. Use nix-build from the doc/ folder to build the manual.
7. Preview the manual on your computer at http://0.0.0.0:8000/manual.html after running from doc/ folder:

nix-shell -p python3 --run 'python3 -m http.server --directory ./result/share/doc/nixpkgs'

8. When it looks good, submit a PR and reference this issue.

[bryanasdev000]

Hi @ryantm!

Already opened a PR for that (#108917).