There have been plugins in the past to attach documentation to your mappings. Some that I know of are, mentioned here both as alternatives and as possible future references:
This plugin is mostly an amalgamation of all of them. However, the main inspiration has been [vim-leader-guide].
It's main limitation, compared to the original so to speak, is the fact that it only works for normal mode mappings. I don't care enough to add support for visual mode ones. Still, it's on the TODO list.
There's not much that I can say. I wrote this mostly for myself. Still, if you use this and find some bug, or want some feature open an Issue. I'll probably fix/implement it.
- Add docs
- Support visual mode mappings