Add toggleterm extension.

Add # symbol.

lua/lualine/extensions/toggleterm.lua

@@ -0,0 +1,12 @@
+-- Copyright (c) 2020-2021 hoob3rt
+-- MIT license, see LICENSE for more details.
+
+local function toggleterm_statusline() return 'ToggleTerm #' .. vim.b.toggle_number end
+
+local M = {}
+
+M.sections = {lualine_a = {toggleterm_statusline}}
+
+M.filetypes = {'toggleterm'}
+
+return M