Add installation instruction with mise

Hi, I'd like to propose to add another way to install git-bug with mise. The mise is a popular tool/runtime manager and can easily install the git-bug via the aqua repository (ref. https://mise.jdx.dev/dev-tools/backends/aqua.html).

I'm using Ubuntu-family distribution and the other ways didn't work, but mise helped me to avoid building the binary by myself. I think adding mise helps more people try git-bug since mise is platform-agnostic tool.

If users already has mise on their machine, the installation is quite simple.

> mise i aqua:git-bug/git-bug
aqua:git-bug/[email protected] download git-bug_linux_amd64                      30.9 MB 0s [=============>    ] 
aqua:git-bug/[email protected] extract git-bug_linux_amd64                                                     ✔

> git-bug version
git-bug version: v0.10.1

If you're fine, I can also make a PR to update INSTALLATION.md. Thanks.