feature: clear ColorColumn highlight

fix #2

README.md

@@ -42,12 +42,6 @@ require("virt-column").setup()
 
 Please see `:help virt-column.txt`for more details and all possible values.
 
-You probably want to clear the old `ColorColumn` highlight if you use this.
-
-```vim
-highlight clear ColorColumn
-```
-
 ## Thanks
 
 Thank you @francium for the idea.

lua/virt-column/init.lua

@@ -20,6 +20,7 @@ M.setup = function(config)
 
     vim.cmd [[command! VirtColumnRefresh lua require("virt-column").refresh()]]
     vim.cmd [[highlight link VirtColumn Whitespace]]
+    vim.cmd [[highlight clear ColorColumn]]
 
     vim.cmd [[
         augroup VirtColumnAutogroup