administration-guide: fix typo that breaks example command

The ' ' (space) between 'etc/ **/*.txt' resulted in the example command's output
not matching the given example output. Removing this space fixes the command.

docs/administration-guide.rst

@@ -777,7 +777,7 @@ For example:
 
 .. code-block:: console
 
-  pxar:/ > find etc/ **/*.txt --select
+  pxar:/ > find etc/**/*.txt --select
   "/etc/X11/rgb.txt"
   pxar:/ > list-selected
   etc/**/*.txt