Update README to include new requirement

Latest Thunk requires the user to belong to video group. Add this
statement to README.md to notify external users on Github.

Change-Id: Id9843abf09de5b63a3b7c3f7b322bc9099c6ff1a
Signed-off-by: Amber Lin <Amber.Lin@amd.com>


[ROCm/ROCR-Runtime commit: 8bc83e1e9b]

projects/rocr-runtime/README.md

@@ -2,6 +2,8 @@
 
 This repository includes the user-mode API interfaces used to interact with the ROCk driver. Currently supported agents include only the AMD/ATI Fiji family of discrete GPUs.
 
+Starting at 1.7 release, ROCt uses drm render device. This requires the user to belong to video group. Add the user account to video group with "sudo usermod -a -G video _username_" command if the user if not part of video group yet.
+
 #### ROCk Driver
 
 The ROCt library is not a standalone product and requires that you have the correct ROCk driver set installed. We recommend reading the full compatibility and installation details which are available in the ROCk github: