[Docs] Add Note to Readme-Template about Variable Espansion (#10983)

* add note with Espansion VarNames

* add context of Name

docs/content/doc/advanced/customizing-gitea.en-us.md

@@ -235,6 +235,9 @@ Locales may change between versions, so keeping track of your customized locales
 
 To add a custom Readme, add a markdown formatted file (without an `.md` extension) to `custom/options/readme`
 
+**NOTE:** readme templates support **variable expansion**.  
+currently there are `{Name}` (name of repository), `{Description}`, `{CloneURL.SSH}` and `{CloneURL.HTTPS}`
+
 ### Reactions
 
 To change reaction emoji's you can set allowed reactions at app.ini