fix: quotes for username on Windows

Author: lechnerc77

released/SAP-Inside-Tracks/SITBLR_JUNE_2025/README.md

@@ -21,9 +21,9 @@ The last step in the setup is the export of the environment variables that are r
 - Windows:
 
     ```pwsh
-    $env:BTP_USERNAME=<your SAP BTP username>
+    $env:BTP_USERNAME='<your SAP BTP username>'
     $env:BTP_PASSWORD='<your SAP BTP password>'
-    $env:CF_USER=<your SAP BTP username>
+    $env:CF_USER='<your SAP BTP username>'
     $env:CF_PASSWORD='<your SAP BTP password>'
     ```