Set 'desc' opt when registering keymaps

[vicecaycedo]

Feature description

When registering keymaps, an optional 'desc' opt can be used to provide a description of the mapping.

Plugins like https://github.com/folke/which-key.nvim can then use this description.

Describe the solution you'd like

It would be helpful if the nvim-bqf mappings were set with descriptions provided.

For example, the description for 'zn' could be 'create a new list for signed items'

Additional context

No response

[kevinhwang91]

1. Set keymap with desc requires a higher Neovim version;
2. I don't use descriptions for keymaps;

However, PR is welcome.