Help: Add release note for C++ 17 support

Closes: #16468

Help/release/dev/features-c++17.rst

@@ -0,0 +1,6 @@
+features-c++17
+--------------
+
+* The :manual:`Compile Features <cmake-compile-features(7)>` functionality
+  is now aware of C++ 17.  No specific features are yet enumerated besides
+  the ``cxx_std_17`` meta-feature.