local changes reverted

CONTRIBUTING.md

@@ -16,7 +16,7 @@ We recommend you use [Vagrant](https://www.vagrantup.com/intro/getting-started/i
 With Vagrant set up, the following should boot up Mail-in-a-Box inside a virtual machine:
 
     $ vagrant up --provision
-
+_If you're seeing an error message about your *IP address being listed in the Spamhaus Block List*, simply uncomment the `export SKIP_NETWORK_CHECKS=1` line in `Vagrantfile`. It's normal, you're probably using a dynamic IP address assigned by your Internet provider–they're almost all listed._
 
 
 ### Modifying your `hosts` file