docs: vim.g.no_plugin_maps to avoid conflicts

[kiyoon]

1. vim.g.no_python_maps or vim.g.no_plugin_maps to avoid conflicts. This actually got me because it seems totally working but actually is broken (like repeatable move etc. won't work)
   • A better way is to overwrite the buffer mappings, but it will be too difficult to explain in the main docs unless we actually provide a convenience function that helps mapping.
2. nvim-next doesn't support main branch of this plugin, thus removed.
3. I think it's unintuitive that "move function" uses ]m and "select function" uses af, if. The standard seems to be using am and im for selecting function as per https://github.com/neovim/neovim/blob/master/runtime/ftplugin/ruby.vim . I know this is just an example, but keeping the main doc following the common convention helps a lot.

[clason]

CI is fixed. (Do you want to squash your commits?)