Update readme with directions on using cookbook

See merge request !3

Make real user

So troubleshooting errors is easier (can use sudo su instead of sudo -u everytime)

/cc @dzaporozhets

See merge request !2

This reverts commit 923e8a31.

Source:
https://github.com/chef/omnibus-software/blob/2e26be554787803214ba9525b6b4214b5c7b6d43/config/software/cacerts.rb

Make instructions obvious

/cc @jacobvosmaer

See merge request !1