Mark PLANon DocuPen RC800 as supported by gPhoto2.

Docupen RC800 support was merged into libgphoto:
https://github.com/gphoto/libgphoto2/pull/533

doc/descriptions/unsupported.desc

@@ -1932,7 +1932,7 @@
 :interface "USB"
 :usbid "0x18dd" "0x1000"
 :status :unsupported
-:comment "Probably not supported. No details known."
+:comment "Supported by gPhoto2."
 
 :model "DocuPen R700"
 :url "unsupported/planon-docupen-r700.html"