Update the placeholder readme to be less deceptive.

Author: rpavlik

OSVR-Unity/Assets/Plugins/x86/README.txt

@@ -1,10 +1 @@
-The OSVR-Unity plugin requires the following files in this directory:
-
-- `osvrClientKit.dll`
-- `osvrClient.dll`
-- `osvrUtil.dll`
-- `osvrTransform.dll`
-
-In the typical case, where the Managed-OSVR source is separately compiled, this directory also must contain:
-
-- `ClientKit.dll`
+Placeholder for OSVR-Core client libraries built for Windows, 32-bit.