docs(pick): add usage example to ui_select()

Author: echasnovski

doc/mini-pick.txt

@@ -1047,6 +1047,10 @@ Implements the required by `vim.ui.select()` signature. Plus allows extra
 Notes:
 - `on_choice` is called when target window is current.
 
+Usage ~
+>lua
+  vim.ui.select = MiniPick.ui_select
+<
 ------------------------------------------------------------------------------
                                                               *MiniPick.builtin*
                                `MiniPick.builtin`

lua/mini/pick.lua

@@ -1224,6 +1224,10 @@ end
 ---
 --- Notes:
 --- - `on_choice` is called when target window is current.
+---
+---@usage >lua
+---   vim.ui.select = MiniPick.ui_select
+--- <
 MiniPick.ui_select = function(items, opts, on_choice)
   local format_item = opts.format_item or H.item_to_string
   local items_ext = {}