ansible: move information about firewall config (#2149)

Setting up the Firewall is one of the manual steps that must be done
after ansibling a new Jenkins worker, so it should be in MANUAL_STEPS.

ansible/MANUAL_STEPS.md

@@ -1,5 +1,6 @@
 # Manual steps required to setup machines
 
+* [Firewall Config](#adding-firewall-entries-for-jenkins-workers)
 * [Release machines](#release-*-machines)
 * [RHEL7-s390x](#RHEL7-s390x)
   * [V8 Build Tools](#V8-build-tools)
@@ -22,6 +23,24 @@
   * [NFS boot](#NFS-boot)
 
 
+## Adding firewall entries for Jenkins workers
+
+Workers must be added to the firewall config before they will be able
+to connect to the Jenkins master.
+
+You must be part of the infra group and have setup the ssh keys and config file
+beforehand.
+
+To add an entry do the following:
+
+* ssh to the ci master: `ssh ci`
+* save the current config to a temporary file: `iptables-save >foo`
+* edit the temporary file with your favorite editor. Use one of
+  the existing lines as a template and add a new entry at the end
+  of the list of hosts just before the second `COMMIT` line near
+  the end of the file.
+* restore the config from the temporary file: `iptables-restore foo`
+* remove the temporary file: `rm foo`
 
 ## `release-*` machines