usb_device-msd test: docs update

Author: maciejbocianski

TESTS/usb_device/msd/README.md

@@ -10,3 +10,12 @@ Test run command:
 ```bash
 mbed test -t COMPILER -m TARGET -n tests-usb_device-msd
 ```
+
+
+## Windows 8/10:
+By default Windows 8 and 10 access and write to removable drives shortly after they are connected. It's caused by drive indexing mechanisms. Because disk used in test has only 64kB its content can be easily corrupted by writing large files, what actually was encountered during test runs.
+
+To prevent Windows from writing to removable drives on connect drive indexing can be turned off with the following procedure:
+- Start the program "gpedit.msc"
+- Navigate to "Computer Configuration \ Administrative Templates \ Windows Components \ Search"
+- Enable the policy "Do not allow locations on removable drives to be added to  libraries."