[Bug other/121958] Document requirements for updating *opt.urls; advertised method does not work

[dmalcolm at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121958

--- Comment #5 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
The patch doesn't contain documentation for the new option.

Looks like there's a bug in regenerate-opt-urls.py where it fails to emit a
comment mentioning options with no documentation.