cmTarget: Improve INCLUDE_DIRECTORIES property docs (#13188).

Note that relative paths should not be added directly.

Help/prop_tgt/INCLUDE_DIRECTORIES.rst

@@ -5,17 +5,20 @@ List of preprocessor include file search directories.
 
 This property specifies the list of directories given so far to the
 include_directories command.  This property exists on directories and
-targets.  In addition to accepting values from the include_directories
+targets.  In addition to accepting values from the :command:`include_directories`
 command, values may be set directly on any directory or any target
-using the set_property command.  A target gets its initial value for
+using the :command:`set_property` command.  A target gets its initial value for
 this property from the value of the directory property.  A directory
 gets its initial value from its parent directory if it has one.  Both
 directory and target property values are adjusted by calls to the
-include_directories command.
+:command:`include_directories` command.
 
 The target property values are used by the generators to set the
-include paths for the compiler.  See also the include_directories
-command.
+include paths for the compiler.  See also the :command:`include_directories`
+and :command:`target_include_directories` commands.
+
+Relative paths should not be added to this property directly. Use one of
+the commands above instead to handle relative paths.
 
 Contents of INCLUDE_DIRECTORIES may use "generator expressions" with the
 syntax "$<...>".  See the :manual:`cmake-generator-expressions(7)` manual for