Centralize External-Services documentation

Deduplicate documentation on external services

Bug: Issue 13059
Change-Id: Ibf5948a0c03daa70bc18c6ef493348414f725cbe
diff --git a/README.md b/README.md
index 6f3bd67..69bf466 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,7 @@
 - [Overview](#overview)
 - [Pre-requisites](#pre-requisites)
 - [Templates](#templates)
+- [External Services](#external-services)
 
 ## Overview
 
@@ -36,3 +37,22 @@
 * [Standalone Gerrit master sandbox with LDAP authentication](/single-master/README.md)
 * [Gerrit master and slave sandbox with LDAP authentication](/master-slave/README.md)
 * [Gerrit dual-master in HA sandbox with LDAP authentication](/dual-master/README.md)
+
+## External services
+
+This is a list of external services that you might need to setup your stack and some suggestions
+on how to easily create them.
+
+#### SMTP Server
+
+If you need to setup a SMTP service Amazon Simple Email Service can be used.
+Details how setup Amazon SES can be found [here](https://docs.aws.amazon.com/ses/latest/DeveloperGuide/send-email-set-up.html).
+
+To correctly setup email notifications Gerrit requires ssl protocol on default port 465 to
+be enabled on SMTP Server. It is possible to setup Gerrit to talk to standard SMTP port 25
+but by default all EC2 instances are blocking it. To enable port 25 please follow [this](https://aws.amazon.com/premiumsupport/knowledge-center/ec2-port-25-throttle/) link.
+
+#### LDAP Server
+
+If you need a testing LDAP server you can find details on how to easily
+create one in the [LDAP folder](ldap/README.md).
diff --git a/dual-master/README.md b/dual-master/README.md
index b7a48ff..fd751e3 100644
--- a/dual-master/README.md
+++ b/dual-master/README.md
@@ -131,24 +131,10 @@
 * HTTP `8080`
 * SSH `29418`
 
-# External services
+### External Services
 
-This is a list of external services that you might need to setup your stack and some suggestions
-on how to easily create them.
-
-## SMTP Server
-
-If you need to setup a SMTP service Amazon Simple Email Service can be used.
-Details how setup Amazon SES can be found [here](https://docs.aws.amazon.com/ses/latest/DeveloperGuide/send-email-set-up.html).
-
-To correctly setup email notifications Gerrit requires ssl protocol on default port 465 to
-be enabled on SMTP Server. It is possible to setup Gerrit to talk to standard SMTP port 25
-but by default all EC2 instances are blocking it. To enable port 25 please follow [this](https://aws.amazon.com/premiumsupport/knowledge-center/ec2-port-25-throttle/) link.
-
-## LDAP Server
-
-If you need a testing LDAP server you can find details on how to easily
-create one in the [LDAP folder](../ldap/README.md).
+If you need to setup some external services (maybe for testing purposes, such as SMTP or LDAP),
+you can follow the instructions [here](../README.md#external-services)
 
 ### Docker
 
diff --git a/master-slave/README.md b/master-slave/README.md
index 642fd01..2de0793 100644
--- a/master-slave/README.md
+++ b/master-slave/README.md
@@ -145,24 +145,10 @@
 * HTTP `9080`
 * SSH `39418`
 
-# External services
+### External Services
 
-This is a list of external services that you might need to setup your stack and some suggestions
-on how to easily create them.
-
-## SMTP Server
-
-If you need to setup a SMTP service Amazon Simple Email Service can be used.
-Details how setup Amazon SES can be found [here](https://docs.aws.amazon.com/ses/latest/DeveloperGuide/send-email-set-up.html).
-
-To correctly setup email notifications Gerrit requires ssl protocol on default port 465 to
-be enabled on SMTP Server. It is possible to setup Gerrit to talk to standard SMTP port 25
-but by default all EC2 instances are blocking it. To enable port 25 please follow [this](https://aws.amazon.com/premiumsupport/knowledge-center/ec2-port-25-throttle/) link.
-
-## LDAP Server
-
-If you need a testing LDAP server you can find details on how to easily
-create one in the [LDAP folder](../ldap/README.md).
+If you need to setup some external services (maybe for testing purposes, such as SMTP or LDAP),
+you can follow the instructions [here](../README.md#external-services)
 
 ## Monitoring
 
diff --git a/single-master/README.md b/single-master/README.md
index d5a1223..43f6d4a 100644
--- a/single-master/README.md
+++ b/single-master/README.md
@@ -110,24 +110,10 @@
 
 The available ports are `8080` for HTTP and `29418` for SSH.
 
-# External services
+### External Services
 
-This is a list of external services that you might need to setup your stack and some suggestions
-on how to easily create them.
-
-## SMTP Server
-
-If you need to setup a SMTP service Amazon Simple Email Service can be used.
-Details how setup Amazon SES can be found [here](https://docs.aws.amazon.com/ses/latest/DeveloperGuide/send-email-set-up.html).
-
-To correctly setup email notifications Gerrit requires ssl protocol on default port 465 to
-be enabled on SMTP Server. It is possible to setup Gerrit to talk to standard SMTP port 25
-but by default all EC2 instances are blocking it. To enable port 25 please follow [this](https://aws.amazon.com/premiumsupport/knowledge-center/ec2-port-25-throttle/) link.
-
-## LDAP Server
-
-If you need a testing LDAP server you can find details on how to easily
-create one in the [LDAP folder](../ldap/README.md).
+If you need to setup some external services (maybe for testing purposes, such as SMTP or LDAP),
+you can follow the instructions [here](../README.md#external-services)
 
 ### Docker