Help: Add notes for topic 'xcode-xctest'

Help/release/dev/xcode-xctest.rst

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+xcode-xctest
+------------
+
+* On OS X, CMake learned to create XCTest bundles to test Frameworks
+  and App Bundles within Xcode.  The :module:`FindXCTest` module
+  provides convenience functions to handle :prop_tgt:`XCTEST` bundles.