add powershell echo geode_sdk example

Author: Cvolton

getting-started/sdk.md

@@ -13,9 +13,12 @@ geode sdk install
 ```
 This *should* set the `GEODE_SDK` enviroment variable, which can you test after restarting your terminal:
 ```bash
-# On windows
+# On Windows CMD
 echo %GEODE_SDK%
 
+# On Windows PowerShell
+echo $env:GEODE_SDK
+
 # Elsewhere
 echo $GEODE_SDK
 ```