Added installation instructions using Mise

[offbyone]

Summary

This PR enhances the README by adding a new section explaining how to install and manage the GitHub MCP Server using Mise. The steps cover:

• Installing Mise from its website
• Using Mise to install the GitHub MCP server with a single command

This makes the setup more flexible by offering an alternative method, particularly helpful for managing dependencies in a streamlined way.

Linked Issue

Closes issue #302.

[Copilot]

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

[offbyone]

For the record, the initial PR here is not good; the LLM tool that generated this gleefully deleted the entire README other than the change I was trying to make :D

[williammartin]

Thanks for the PR @offbyone but I'm going to close this for now.

We're not that keen on recommending installation mechanisms we don't own, to give ourselves flexibility as we continue learning. For the moment we're going to commit to homebrew as our only recommended third party mechanism.

I could see a future in which we have a community supported section as per the gh CLI https://github.com/cli/cli/blob/trunk/docs/install_linux.md#unofficial-community-supported-methods, but that's not right now.