docs: start documenting previewers (#574)

Co-authored-by: Muhammed Zakir <MuhammedZakir@users.noreply.github.com>

lua/telescope/init.lua

@@ -12,6 +12,7 @@ local telescope = {}
 --- Telescope.nvim is a plugin for fuzzy finding and neovim. It helps you search,
 --- filter, find and pick things in Lua.
 ---
+--- <pre>
 --- To find out more:
 --- https://github.com/nvim-telescope/telescope.nvim
 ---
@@ -19,6 +20,7 @@ local telescope = {}
 ---   :h telescope.builtin
 ---   :h telescope.layout
 ---   :h telescope.actions
+--- </pre>
 ---@brief ]]
 
 ---@tag telescope.nvim
@@ -50,7 +52,7 @@ function telescope.load_extension(name)
   return _extensions.load(name)
 end
 
---- Use telescope.extensions to reference any extensions within your configuration.
+--- Use telescope.extensions to reference any extensions within your configuration. <br>
 --- While the docs currently generate this as a function, it's actually a table. Sorry.
 telescope.extensions = require('telescope._extensions').manager
 
@@ -60,16 +62,19 @@ telescope.__format_setup_keys = function()
   local names = vim.tbl_keys(descriptions)
   table.sort(names)
 
-  local result = { "", "", "Valid keys for {opts.defaults}" }
+  local result = { "<pre>", "", "Valid keys for {opts.defaults}" }
   for _, name in ipairs(names) do
     local desc = descriptions[name]
 
     table.insert(result, "")
     table.insert(result, string.format("%s*telescope.defaults.%s*", string.rep(" ", 70 - 20 - #name), name))
     table.insert(result, string.format("%s: ~", name))
-    table.insert(result, string.format("    %s", desc))
+    for _, line in ipairs(vim.split(desc, '\n')) do
+      table.insert(result, string.format("    %s", line))
+    end
   end
 
+  table.insert(result, '</pre>')
   return result
 end