docs: add Windows PowerShell equivalents for environments and scripting (#20333)

docs/cli/tutorials/skills-getting-started.md

@@ -14,10 +14,18 @@ responding correctly.
 
 1.  Run the following command to create the folders:
 
+    **macOS/Linux**
+
     ```bash
     mkdir -p .gemini/skills/api-auditor/scripts
     ```
 
+    **Windows (PowerShell)**
+
+    ```powershell
+    New-Item -ItemType Directory -Force -Path ".gemini\skills\api-auditor\scripts"
+    ```
+
 ### Create the definition
 
 1.  Create a file at `.gemini/skills/api-auditor/SKILL.md`. This tells the agent