Add CLI documentation with usage and alias instructions

[guplem]

Summary

• Adds a new docs/cli.md with a quick CLI usage showcase and shell alias instructions (PowerShell, Bash/Zsh, Fish)
• Adds a brief "Command Line Interface" section to the README linking to the doc

Test plan

• Verify docs/cli.md renders correctly
• Verify the README link works

[pol-rivero]

I considered naming it github-plus back when I was renaming everything to make this fork compatible with the upstream, but at the end I decided to use github-desktop-plus-cli for consistency and to ensure it would never conflict with other programs.

My rationale is that if users want to use a shorter name, they can easily create an alias in their shell configs (they can even name it just github if they want to return to the old name). The project should provide a sufficiently unique name that makes sense as a default. I don't think github-plus is sufficiently unique.

If you tell me which shell you are using, I can search the corresponding instructions for creating an alias. :)

[guplem]

Fair enough, that makes sense! I hadn't considered the uniqueness angle.

Would it be useful to add a short section to the README with instructions on how to create a shell alias? That way users who want a shorter command can set it up easily regardless of their OS/shell.

[guplem]

I've updated the PR to add a "Creating a CLI alias" section to the README instead, with instructions for PowerShell, Bash/Zsh, and Fish.

[pol-rivero]

Would it be useful to add a short section to the README with instructions on how to create a shell alias?

Absolutely! In fact, right now I think we are never explaining the fact that the CLI command even exists, so it would make sense to have a section with a quick showcase and instructions for creating the alias.

Right now, I think the README is already a bit long, so maybe we could create a separate markdown file and link to it in a small readme section (just like we did in the Common issues section).

[guplem]

I've updated the PR: moved the content to a separate docs/cli.md (following the same pattern as docs/known-issues.md) with a CLI usage showcase and alias instructions. The README now just has a brief section linking to it.

[pol-rivero]

Great job as always :)