Update README.md

Author: rcalago

core-kotlin-modules/core-kotlin-io/README.md

@@ -10,3 +10,4 @@ This module contains articles about core Kotlin I/O.
 - [Writing InputStream to File in Kotlin](https://www.baeldung.com/kotlin/inputstream-to-file)
 - [Rename a File in Kotlin](https://www.baeldung.com/kotlin/file-rename)
 - [Delete the Contents of a File in Kotlin](https://www.baeldung.com/kotlin/delete-file-content)
+- [File Upload in Kotlin](https://www.baeldung.com/kotlin/file-upload)