feat(picker): allow appending original window cword to prompt (#2878)

* feat(picker): allow appending original window cword to prompt

* add default mapping and document

* [docgen] Update doc/telescope.txt
skip-checks: true

* add mapping to README

also format README

* oops

* [docgen] Update doc/telescope.txt
skip-checks: true

---------

Co-authored-by: Github Actions <actions@github>

lua/telescope/pickers.lua

@@ -529,6 +529,7 @@ function Picker:find()
   self:reset_selection()
 
   self.original_win_id = a.nvim_get_current_win()
+  self.original_cword = vim.fn.expand "<cword>"
 
   -- User autocmd run it before create Telescope window
   vim.api.nvim_exec_autocmds("User", { pattern = "TelescopeFindPre" })
@@ -845,7 +846,13 @@ function Picker:delete_selection(delete_cb)
   end, 50)
 end
 
-function Picker:set_prompt(text)
+---@param text string text to set as prompt
+---@param reset boolean? whether to replace prompt with text entirely or just append
+function Picker:set_prompt(text, reset)
+  reset = vim.F.if_nil(reset, true)
+  if not reset then
+    text = self:_get_prompt() .. text
+  end
   self:reset_prompt(text)
 end