update NEWS, mention known issues

NEWS.md

@@ -2,7 +2,7 @@
 
 ## New features
   * Accept prefill credentials in base64 form #153 #811
-  * Indroduce AAC encoder to audio redirection (requires Windows 10)
+  * Indroduce AAC encoder to audio redirection (requires Windows 10 client)
 
 ## Bugfixes
   * Fix ocasional SEGV in drive redirection #838
@@ -18,6 +18,10 @@
   * Add a PAM file for FreeBSD #824
   * Several refactorings and cosmetic changes
 
+## Known issues
+  * Windows 10 (1703) shows black blank screen in RemoteFX mode
+   * This issue is already fixed at Insider Preview build 16273
+
 # Release notes for xrdp v0.9.3.1 (2017/08/16)
 
 This release fixes a trivial packaging issue #848 occurred in v0.9.3.  The issue only affects systemd systems.  This release is principally for distro packagers or users who compile & install xrdp from source.