home: vim: telescope: add 'which-key' mapping

This opens a little preview window with different mappings for
telescope.

home/vim/plugin/settings/telescope.vim

@@ -5,6 +5,7 @@ telescope.setup({
     defaults = {
         mappings = {
             i = {
+                ["<C-h>"] = "which_key",
                 -- I want the normal readline mappings rather than scrolling
                 ["<C-u>"] = false,
             }