create a `good first issue` label and label issues that would be good tasks for newbies to take up

- [x] I have read through the manual page (`man fzf`)
- [x] I have the latest version of fzf
- [x] I have searched through the existing issues

## Info

- OS
- [ ] Linux
- [x] Mac OS X
- [ ] Windows
- [ ] Etc.
- Shell
- [ ] bash
- [x] zsh
- [ ] fish

## Problem / Steps to reproduce

Hi \@junegunn and co,

I would just like to ask you to consider creating a `good first issue` label, and label those issues which would be good tasks to introduce a newcomer to the codebase. I love using fzf, and would love to contribute!

Tons of other projects adopt this approach, though I can't speak to the success or failure of it. But with the sheer number of projects that use it, I would think it would be a net benefit. See a good list here: https://github.com/MunGell/awesome-for-beginners

Cheers!

No source files or tests are named. Start by reviewing the repository's open issues and contribution guidance, then identify tasks suitable for newcomers. Done means creating the requested GitHub label and applying it to appropriate issues.

Written by the indexing model from the issue text.