docs: Fix various errors

[cgwalters]

Remove references to non-existent commands and incorrect options:

• Remove non-existent bcvk libvirt create command from README
• Remove non-existent bcvk libvirt restart command
• Remove incorrect --autostart flag from libvirt-run examples
• Remove unsupported disk formats (VHD, VMDK) from disk-images.md and really trim down to be clear it just wraps bootc install.
• Remove non-existent --partition option
• Fix --size to correct --disk-size flag throughout

Fix incorrect references:

• Fix binary name from bck to bcvk in docs/HACKING.md and Justfile
• Fix repository URL from cgwalters/bcvk to bootc-dev/bcvk

Fix incomplete content:

• Complete incomplete sentence in README about ephemeral VMs
• Populate empty docs/src/HACKING.md with redirect to ../HACKING.md
• Fix path in docs/src/contributing.md

Assisted-by: Claude Code (Sonnet 4.5)

[gemini-code-assist]

Code Review

This pull request provides a good set of fixes for the documentation, removing incorrect commands, options, and outdated information. The changes make the documentation more accurate. I've added a few suggestions to further improve the readability and usefulness of the documentation, mainly around link formatting and restoring some helpful, corrected examples for the to-disk command.

[gemini-code-assist]

For better readability, it's generally preferred to use a clean name for the link text rather than a relative path. How about using HACKING.md as the link text?

Suggested change

	See [../HACKING.md](../HACKING.md) for development instructions.
	See [HACKING.md](../HACKING.md) for development instructions.

[gemini-code-assist]

For better readability and consistency with other files, it's generally preferred to use a clean name for the link text rather than a relative path. How about using HACKING.md as the link text?

Suggested change

	We welcome contributions to bcvk! Please see [../HACKING.md](../HACKING.md) for detailed development instructions.
	We welcome contributions to bcvk! Please see [HACKING.md](../HACKING.md) for detailed development instructions.

[gemini-code-assist]

While it's great that you're removing incorrect information, this change removes all examples, making the documentation less helpful. The bcvk to-disk command has its own options and workflow that are worth documenting with a few examples.

To improve usability, please consider restoring a few corrected examples to give users a quick and accurate starting point. For example:

# Disk Images

The `to-disk` command creates disk images from bootc containers.
It is a wrapper for [bootc install to-disk](https://bootc-dev.github.io/bootc/man/bootc-install-to-disk.8.html), but provides its own options for disk creation and runs the installation inside an ephemeral VM.

## Examples

### Basic Usage

To create a default raw disk image:
```bash
bcvk to-disk quay.io/fedora/fedora-bootc:42 output.img

Specifying Format and Size

To create a 20GB qcow2 image:

bcvk to-disk --format qcow2 --disk-size 20G quay.io/fedora/fedora-bootc:42 output.qcow2

Custom Filesystem

To use the xfs filesystem:

bcvk to-disk --filesystem xfs quay.io/fedora/fedora-bootc:42 output.img

[jmarrero]

lgtm