show lua-mappings in readme.

Show both the lua-api, and a different set of mappings (since
overloading tab has some annoying side-effects).

README.md

@@ -61,6 +61,9 @@ Neovim >= 0.5 (extmarks)
   Consider watching the repos releases so you're notified when a new version becomes available.
 
 ## Keymaps
+In vimscript, with `<Tab>` for jumping forward/expanding a snippet, `<Shift-Tab>` for
+jumping backward, and `<Ctrl-E>` for changing the current choice when in a
+choiceNode...
 ```vim
 " press <Tab> to expand or jump in a snippet. These can also be mapped separately
 " via <Plug>luasnip-expand-snippet and <Plug>luasnip-jump-next.
@@ -75,6 +78,23 @@ snoremap <silent> <S-Tab> <cmd>lua require('luasnip').jump(-1)<Cr>
 imap <silent><expr> <C-E> luasnip#choice_active() ? '<Plug>luasnip-next-choice' : '<C-E>'
 smap <silent><expr> <C-E> luasnip#choice_active() ? '<Plug>luasnip-next-choice' : '<C-E>'
 ```
+
+... or in lua, with a different set of keys: `<Ctrl-K>` for expanding, `<Ctrl-L>`
+for jumping forward, `<Ctrl-J>` for jumping backward, and `<Ctrl-E>` for
+changing the active choice.
+
+```lua
+vim.keymap.set({"i"}, "<C-K>", function() ls.expand() end, {silent = true})
+vim.keymap.set({"i", "s"}, "<C-L>", function() ls.jump( 1) end, {silent = true})
+vim.keymap.set({"i", "s"}, "<C-J>", function() ls.jump(-1) end, {silent = true})
+
+vim.keymap.set({"i", "s"}, "<C-E>", function()
+	if ls.choice_active() then
+		ls.change_choice(1)
+	end
+end, {silent = true})
+```
+
 `nvim-cmp`'s wiki also contains [an example](https://github.com/hrsh7th/nvim-cmp/wiki/Example-mappings#luasnip) for
 setting up a super-tab-like mapping.