docs: Product key (#279)

Author: kroese

readme.md

@@ -207,11 +207,11 @@ The example folder `./example` will be available as ` \\host.lan\Data`.
 
 ### How do I set the product key?
 
-  By default, an evaluation version of Windows will be installed, but if you have product key you can add a `KEY` variable like this (before installation):
+  By default, an evaluation version of Windows will be installed, but if you have a product key you can add a `KEY` variable like this (before installation):
 
   ```yaml
   environment:
-    KEY: "XXXXX-XXXXX-XXXXX-XXXXX-XXXXX"
+    KEY: "xxxxx-xxxxx-xxxxx-xxxxx-xxxxx"
   ```
 
 ### How do I install a custom image?