Clarify External Volume Support

### Description

When running a Colima instance using the Docker runtime, any mounts made do not map to external directories present on the host machine. It will create a blank or even a shadow copy of the directory structure but not contain/update any of the files expected on said host directory.

This issue persists the same way even when the command `limactl edit colima` is run and the external mount added, which seems to overwrite one of the default mounts as well, causing catastrophic issues to containers/projects already existing in colima.

### Version

Colima Version: 0.4.6
Lima Version: 0.13.0
Qemu Version: 7.1.0

### Operating System

- [X] macOS Intel
- [ ] macOS M1
- [ ] Linux

### Reproduction Steps

1. Either using `docker run` or a Docker Compose project, add a volume mount that maps to an existing directory on the host machine.
2. Make sure the mount is writable in `limactl edit colima`
3. When attempting to access files in the now running Docker container, attempt to access the mounted directory.

### Expected behaviour

The directory would contain the expected files and read/write to the actual directory on the host.

### Additional context

This affects services like Nextcloud, calibre-web, and other services dependent on large amounts of storage that can’t solely be contained in a VM.