Fix broken links (#1)

- Always use a relative markdown link so that we can jump even if we edit it in local env or read it in code hosting server.

Reviewed-on: https://gitea.com/gitea/docs/pulls/1

versioned_docs/version-1.22/administration/external-renderers.md

@@ -24,7 +24,7 @@ it is just a matter of:
 - add some configuration to your `app.ini` file
 - restart your Gitea instance
 
-This supports rendering of whole files. If you want to render code blocks in markdown you would need to do something with javascript. See some examples on the [Customizing Gitea](administration/customizing-gitea.md) page.
+This supports rendering of whole files. If you want to render code blocks in markdown you would need to do something with javascript. See some examples on the [Customizing Gitea](../administration/customizing-gitea.md) page.
 
 ## Installing external binaries