Merge pull request #4304 from baywet/chore/add-ms-extensions-link

docs: adds ms extensions repo link

Author: lornajane

registries/_namespace/ms.md

@@ -1,12 +1,12 @@
 ---
 owner: DarrelMiller
 issue: 
-description: Extensions created and used by Microsoft
+description: Extensions [created and used by Microsoft](https://github.com/microsoft/OpenAPI/blob/main/extensions/index.md)
 layout: default
 ---
 
 {% capture summary %}
-The `x-{{page.slug}}-` prefix is reserved for extensions created by Microsoft. These extensions are available for use by anyone.
+The `x-{{page.slug}}-` prefix is reserved for [extensions created by Microsoft](https://github.com/microsoft/OpenAPI/blob/main/extensions/index.md). These extensions are available for use by anyone.
 {% endcapture %}
 
 {% include namespace-entry.md summary=summary %}