Visual mode yank not work for clipboard `"+`

[atauzki]

tested on wsl, when open a file, yank some lines on visual mode with "+y
then see the content of :reg, the :+ remains unchanged.

I commented the clipboard related code and installed xclip, it works.

[Shaobin-Jiang]

Seems that commenting the code is unnecessary. Installing xclip alone solves the problem for me. Maybe the instruction about xclip not required on wsl should be removed from README.