gh help manual entries are missing that they're in `help`

### Describe the bug

1. https://cli.github.com/manual/gh_help_environment doesn't have a link to https://cli.github.com/manual/gh_help in see also
2. the section says `gh environment`, but there's no such command
3. the manual for https://cli.github.com/manual/gh_help is more or less useless

### Steps to reproduce the behavior

1. Visit https://cli.github.com/manual/gh_help_environment
2. See `gh environment`
3. See `See also` `gh`

4. Visit https://cli.github.com/manual/gh_help

### Expected vs actual behavior

* `gh help environment`
* See also `gh help`
* See list of help items in https://cli.github.com/manual/gh_help