Add description of the properties feature.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@11638 a1c6a512-1295-4272-9138-f99709370657

manual/rockbox_interface/playback.tex

@@ -129,6 +129,10 @@ each option pertains both to files and directories):
   for more details on viewers.
 \item [Create Directory.]
   Create a new folder in the current folder on the disk.
+\item [Properties.]
+  Shows properties such as size and the time and date of the last modification
+  for the selected file. If used on a directory, the number of files and sub
+  directories in that directory will be shown, as well as the total size.
 \end{description}
 
 \subsection{\label{ref:Playlistsubmenu}Playlist Submenu}