Procmail with Qmail

I'm having a problem compiling the qmail patch (procmail-maildir.patch)
with procmail.

Actually the problem is I don't know how to install the patch.  I read
through the pmtips and it just says to get the patch.  The qmail home page
doesn't tell how to install the patch.

Can anyone help me out?

Thanks in advance.

Caedmon