docs: add a changelog entry for updated version requirements (#1444)

- also updates the error message to point to it

doc/telescope_changelog.txt

@@ -119,5 +119,16 @@ Guide to switch over to plenary.path
         before: require("telescope.path").read_file_async(filepath, callback)
         now:    require("plenary.path"):new(filepath):read(callback)
 
+                                                    *telescope.changelog-1406*
+
+Date: November 4, 2021
+PR: https://github.com/nvim-telescope/telescope.nvim/pull/1406
+
+Telescope requires Neovim release 0.5.1 or a recent nightly
+
+Due to making use of newly implemented extmark features, Telescope now
+requires users to be on Neovim 0.5.1 (the most recent stable version) or on
+the LATEST version of Neovim nightly.
+
 
  vim:tw=78:ts=8:ft=help:norl:

plugin/telescope.vim

@@ -1,5 +1,5 @@
 if !has('nvim-0.5.1')
-  echoerr "Telescope.nvim requires at least nvim-0.5.1. Please update or uninstall"
+  echoerr "Telescope.nvim requires at least nvim-0.5.1. See `:h telescope.changelog-1406`"
   finish
 end