docs(README.md): Add human readable description to keymap

[rodrigc]

Description

In the readme, I think it would be nice to add human readable descriptions to the keymaps.

See: https://neovim.io/doc/user/lua.html#vim.keymap.set()

and documentation for the desc parameter:
https://neovim.io/doc/user/api.html#nvim_set_keymap()

This makes the output for tools like which-key.nvim look nicer.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• use which-key.nvim to look at the keymaps

Configuration:

• Neovim version (nvim --version):

NVIM v0.10.1
Build type: Release
LuaJIT 2.1.1720049189
Run "nvim -V1 -v" for more info

• Operating system and version:

macOS 14.6.1

Checklist:

• My code follows the style guidelines of this project (stylua)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (lua annotations)

[jamestrew]

thanks!