Cygwin: doc: warn about unprivileged access to raw devices

Raw devices of partitions may be accessible from unprivileged
processes, for example if connected via USB.

Signed-off-by: Christian Franke <[email protected]>
(cherry picked from commit 8065978ff838f393dfbc7e61374df56f1f157847)

Author: chrfranke

winsup/doc/specialnames.xml

@@ -368,7 +368,15 @@ handle the information.  <emphasis role='bold'>Writing</emphasis> to a raw
 mass storage device you should only do if you
 <emphasis role='bold'>really</emphasis> know what you're doing and are aware
 of the fact that any mistake can destroy important information, for the
-device, and for you.  So, please, handle this ability with care.
+device, and for you.  So, please, handle this ability with care.</para>
+
+<para><emphasis role='bold'>Important:</emphasis> Windows may allow raw read
+<emphasis role='bold'>and write</emphasis> access to partitions (for example
+<filename>/dev/sda2</filename>) even from unprivileged processes.  This is
+usually the case for partitions on "removable" drives like USB flash drives
+or regular SATA/NVMe drives behind USB docking stations.  If
+<command>chkdsk X:</command> works, raw access to the same partition is
+possible from the same user account.
 <emphasis role='bold'>You have been warned.</emphasis></para></note>
 
 <para>