[ci skip] document acceptance test helper method

This comment was previously in our spec_helper_acceptance.rb.
https://github.com/voxpupuli/puppet-zabbix/pull/699/files#diff-174f7dfb508155027cb4c3e9a1840591L5

Author: bastelfreak

spec/support/acceptance/prepare_host.rb

@@ -1,6 +1,8 @@
 def prepare_host
   if fact('os.family') == 'RedHat'
     shell('rm -rf /etc/yum.repos.d/Zabbix*.repo; rm -rf /var/cache/yum/x86_64/*/Zabbix*; yum clean all --verbose')
+    # The CentOS docker image has a yum config that won't install docs, to keep used space low
+    # zabbix packages their SQL file as doc, we need that for bootstrapping the database
     if fact('os.release.major').to_i == 7
       shell('sed -i "/nodocs/d" /etc/yum.conf')
     end