Help: Add Ninja Multi-Config and make generator types into links

Help/prop_tgt/XXX_OUTPUT_DIRECTORY.txt

@@ -3,9 +3,10 @@ Output directory in which to build |XXX| target files.
 This property specifies the directory into which |xxx| target files
 should be built.  The property value may use
 :manual:`generator expressions <cmake-generator-expressions(7)>`.
-Multi-configuration generators (VS, Xcode) append a per-configuration
-subdirectory to the specified directory unless a generator expression
-is used.
+Multi-configuration generators (:ref:`Visual Studio <Visual Studio Generators>`,
+:generator:`Xcode`, :generator:`Ninja Multi-Config`) append a
+per-configuration subdirectory to the specified directory unless a generator
+expression is used.
 
-This property is initialized by the value of the variable
-|CMAKE_XXX_OUTPUT_DIRECTORY| if it is set when a target is created.
+This property is initialized by the value of the
+|CMAKE_XXX_OUTPUT_DIRECTORY| variable if it is set when a target is created.