image-index: define platform.os.features on Windows

Signed-off-by: Akihiro Suda <[email protected]>

Author: AkihiroSuda

image-index.md

@@ -59,7 +59,10 @@ For the media type(s) that this document is compatible with, see the [matrix][ma
 
     - **`os.features`** *array of strings*
 
-        This OPTIONAL property specifies an array of strings, each specifying a mandatory OS feature (for example on Windows `win32k`).
+        This OPTIONAL property specifies an array of strings, each specifying a mandatory OS feature.
+        For Windows, image indexes SHOULD use, and implementations SHOULD understand the following values:
+		- `win32k`: image requires `win32k.sys` on the host (Note: `win32k.sys` is missing on Nano Server)
+        Convention for other features SHOULD be submitted to this specification for standardization.
 
     - **`variant`** *string*