Help: Add hint to required VS 2017 component for C++/CLI support

Help/prop_tgt/COMMON_LANGUAGE_RUNTIME.rst

@@ -16,4 +16,7 @@ Supported values: ``""``, ``"pure"``, ``"safe"``
 This property is only evaluated :ref:`Visual Studio Generators` for
 VS 2010 and above.
 
+To be able to build managed C++ targets with VS 2017 and above the component
+``C++/CLI support`` must be installed, which may not be done by default.
+
 See also :prop_tgt:`IMPORTED_COMMON_LANGUAGE_RUNTIME`