Use `chformal` as example, comparing the `autocmd` output with `ChformalPass::formal_help()`, the json dump from the `ContentListing`, the command line output, and the RST generated (using `autocmd_rst`).
Includes bullet points on each step for more information.
Should eventually end up in `yosys_internals/extending_yosys/contributing.rst`, but it currently lives in `cmd/index_internal.rst` to avoid merge conflicts since cell help documentation is still WIP.
Also exports chformal source and help output to `docs/source/generated` during `make docs/prep`.
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