Document usage with neovim

**Is your feature request related to a problem? Please describe.**
There's been some discussion of lazygit usage within neovim:
* https://github.com/jesseduffield/lazygit/issues/996
* https://github.com/jesseduffield/lazygit/discussions/1956

There is also a popular plugin: https://github.com/kdheepak/lazygit.nvim

We should have something in our readme pointing users in the right direction when it comes to neovim integration. That may be as simple as linking to the above plugin, or giving advice about how to set editor commands with the remote neovim instance, etc.