Help: Clarify wording of set_directory_properties docs

Help/command/set_directory_properties.rst

@@ -1,12 +1,11 @@
 set_directory_properties
 ------------------------
 
-Set a property of the directory.
+Set properties of the current directory and subdirectories in key-value pairs.
 
 ::
 
   set_directory_properties(PROPERTIES prop1 value1 prop2 value2)
 
-Set a property for the current directory and subdirectories. See
-:ref:`Directory Properties` for the list of properties known
-to CMake.
+See :ref:`Directory Properties` for the list of properties known to CMake
+and their individual documentation for the behavior of each property.