Updated readme.

Author: hozuki

README.md

@@ -24,7 +24,7 @@ A simulator for [THE iDOLM@STER Million Live! Theater Days](https://millionlive.
 
 **Requirements:**
 
-- Windows 7 or later <sup>1</sup>
+- Windows 7 or later <sup>1 2</sup>
 - [.NET Framework 4.5](https://www.microsoft.com/en-us/download/details.aspx?id=42642)
 - Visual C++ 2010 Runtime ([32-bit](https://www.microsoft.com/en-us/download/details.aspx?id=8328) | [64-bit](https://www.microsoft.com/en-us/download/details.aspx?id=13523))
 - [Visual C++ 2015 Runtime](https://www.microsoft.com/en-us/download/details.aspx?id=53587)
@@ -41,6 +41,9 @@ bypassing OS version check (Wine seems to always return an OS major version less
 `MMDeviceEnumerator` still fails to initialize due to COM object creation failure. `MFCreateDxgiDeviceManager()`
 is just a stub. So up till September 2017, MilliSim is only able to run on Windows.
 
+<sup>2</sup> Playing a background video is not yet (version: v0.2) supported on Windows 7. It is
+supported on Windows 8 or later.
+
 ## Building
 
 **Requirements:**