Help: Add notes for topic 'wix-reg-install-dir'

Help/release/dev/wix-reg-install-dir.rst

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+wix-reg-install-dir
+-------------------
+
+* The precompiled Windows binary MSI package provided on ``cmake.org`` now
+  records the installation directory in the Windows Registry under the key
+  ``HKLM\Software\Kitware\CMake`` with a value named ``InstallDir``.