📝 Update YAML introduction

docs/layouts/shortcodes/guides/config-desc.md

@@ -7,7 +7,7 @@ Activated environments go through Platform.sh's build and deploy phases,
 resulting in a fully isolated running site for each activated branch (or pull request) on that repository.
 
 Once an environment is activated, Platform.sh provisions a cluster of containers to deploy your app.
-The configuration of that cluster is controlled by three [YAML files]({{ relref . "/overview/yaml.md" }}):
+The configuration of that cluster is controlled by three [YAML files]({{ relref . "/overview/yaml/_index.md" }}):
 
 - `.platform/routes.yaml` controls how incoming requests are routed to your app, or apps in a multi-app setup.
   It also controls the built-in HTTP cache.

docs/src/create-apps/upgrading.md

@@ -33,7 +33,7 @@ title: "Upgrading"
 
 ## Changes in version 2017.11 (2017-11-09)
 
-* The `!archive` tag in YAML files is now deprecated in favor of the more generic [`!include`](../overview/yaml.md).  For example, the following `services.yaml` snippet:
+* The `!archive` tag in YAML files is now deprecated in favor of the more generic [`!include`](../overview/yaml/_index.md).  For example, the following `services.yaml` snippet:
 
     ```yaml
     mysearch:

docs/src/languages/java/migration.md

@@ -31,7 +31,7 @@ For more details, see [tuning](./tuning.md).
 
 To start a Java application, you need to understand the [Platform.sh structure](/overview/structure.md).
 At minimum, you to configure your [application](../../create-apps/_index.md)
-and have two [YAML files](../../overview/yaml.md) (though they can be blank if you don't need them):
+and have two [YAML files](../../overview/yaml/_index.md) (though they can be blank if you don't need them):
 
 * [Routes](../../define-routes/_index.md)
 * [Services](../../add-services/_index.md)

docs/src/overview/yaml/_index.md

@@ -0,0 +1,13 @@
+---
+title: YAML
+weight: 1
+description: An overview of YAML and its use at Platform.sh.
+aliases:
+  - "/configuration/yaml.html"  
+---
+
+[YAML](https://en.wikipedia.org/wiki/YAML) is a human-readable format for data serialization across languages.
+This means it's a good fit for human-edited configuration files, like those at Platform.sh.
+You can control nearly all aspects of your project's build and deploy pipeline with YAML files.
+
+Learn what YAML is or, if you're already familiar, what custom tags Platform.sh offers.