Help: Add notes for topic 'generalize-LINK_ONLY'

Help/release/dev/generalize-LINK_ONLY.rst

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+generalize-LINK_ONLY
+--------------------
+
+* The :prop_tgt:`INTERFACE_LINK_LIBRARIES` target property now supports
+  a ``$<LINK_ONLY:...>``
+  :manual:`generator expression <cmake-generator-expressions(7)>`.