Help: Clean up INITIALIZE_FROM_VARIABLE define_property() option

INITIALIZE_FROM_VARIABLE is new in CMake 3.23, but the
versionadded note was missing in the original commit. The docs
also failed to mention that the new option only applies to target
properties.

Amends fce24e4f10 (define_property(): Add INITIALIZE_FROM_VARIABLE
argument, 2022-01-13)

Help/command/define_property.rst

@@ -63,7 +63,9 @@ the documentation.
 
   The ``BRIEF_DOCS`` and ``FULL_DOCS`` options are optional.
 
-The ``INITIALIZE_FROM_VARIABLE`` option is followed by the name of a variable
-from which to initialize the property. The variable name must end with the
-property name, must have a prefix before the property name, and must not begin
-with ``CMAKE_`` or ``_CMAKE_``.
+.. versionadded:: 3.23
+
+  The ``INITIALIZE_FROM_VARIABLE`` option specifies a variable from which the
+  property should be initialized. It can only be used with target properties.
+  The ``<variable>`` name must end with the property name, must have a prefix
+  before the property name, and must not begin with ``CMAKE_`` or ``_CMAKE_``.