Merge pull request #652 from AkihiroSuda/platform-os-features

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

Author: stevvooe

image-index.md

@@ -61,7 +61,10 @@ 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.
+        When `os` is `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)
+        When `os` is not `windows`, values are implementation-defined and SHOULD be submitted to this specification for standardization.
 
     - **`variant`** *string*