Add doc type

For CI services examples

doc/ci/services/README.md

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+type: index
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-# GitLab CI Services
+# GitLab CI services examples
 
-GitLab CI uses the `services` keyword to define what docker containers should
-be linked with your base image. Below is a list of examples you may use.
+The [`services`](../docker/using_docker_images.md#what-is-a-service)
+keyword defines a Docker image that runs during a `job` linked to the
+Docker image that the image keyword defines. This allows you to access
+the service image during build time.
+
+The service image can run any application, but the most common use
+case is to run a database container, for example:
 
 - [Using MySQL](mysql.md)
 - [Using PostgreSQL](postgres.md)
 - [Using Redis](redis.md)
-- [Using Other Services](../docker/using_docker_images.md#what-is-a-service)

doc/ci/services/mysql.md

+---
+type: reference
+---
+
 # Using MySQL
 
 As many applications depend on MySQL as their database, you will eventually

doc/ci/services/postgres.md

+---
+type: reference
+---
+
 # Using PostgreSQL
 
 As many applications depend on PostgreSQL as their database, you will

doc/ci/services/redis.md

+---
+type: reference
+---
+
 # Using Redis
 
 As many applications depend on Redis as their key-value store, you will