Help: Add release notes for debugging find commands

Help/release/dev/command_debug_find.rst

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+cmake-debug-find
+----------------
+
+* :manual:`cmake(1)` gained a ``--debug-find`` command line
+  option that can be used to provide information on where find
+  commands searched.
+
+* Variable :variable:`CMAKE_FIND_DEBUG_MODE` was introduced to
+  print extra find call information during the cmake run to standard
+  error. Output is designed for human consumption and not for parsing.