update docs with new sudo instructions

README.md

@@ -20,6 +20,7 @@ The following Ubuntu distributions are supported:
 * trusty
 * xenial
 * bionic
+* focal (coming soon)
 
 
 ## Installing the necessary packages
@@ -48,17 +49,9 @@ The above also installs a daily cron job to update the chroots.
 
 ## Using sudo
 
-In order to run `pbuilder` as a non-root user you need to add the
-following line to `/etc/sudoers`:
+In order to run `pbuilder` as a non-root user you need to tell sudo that
+all users who are members of the `root` group can run cowbuilder.  The
+`su_debuild` module sets this up in sudo for you automatically by adding a
+file to `/etc/sudoers.d` containing this line:
 
     %root    ALL = NOPASSWD: /usr/sbin/cowbuilder
-
-The `su_debuild` module provides a convenience class to do this,
-[`su_debuild::sudo`](manifests/sudo.pp). Here is how you can install all
-the packages, chroots, and set up sudo:
-
-    include su_debuild
-    include su_debuild::sudo
-    class { 'su_debuild::chroots':
-      chroots => [ 'sid', 'stretch', 'jessie', 'bionic']
-    }