The "Command menonics" section in Zed's vim mode documentation made it
seem that the mentioned aliases were available, by default, which isn't
the case. These changes update the documentation to make it clearer that
this is meant to be set on the `command_aliases` setting and provides
and example configuration that users can easily copy and paste into
their settings file.

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Closes #52894

Release Notes:

- N/A

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Co-authored-by: dino <dinojoaocosta@gmail.com>