Add an usage example of BreakBeforeBraces

[djasper]

This change needs to be made to include/clang/Format/Format.h and then the rst file needs to be regenerated with docs/tools/dump_format_style.py.

[sylvestre.ledru]

Thanks. I need more coffee.

[djasper]

Looks good.

docs/ClangFormatStyleOptions.rst

   If ``BreakBeforeBraces`` is set to ``BS_Custom``, use this to specify how
   each individual brace case should be handled. Otherwise, this is ignored.
 
+  .. code-block:: yaml
+
+    # Example of usage:
+    BreakBeforeBraces: Custom
+    BraceWrapping:
+      AfterEnum: true
+      AfterStruct: false
+      SplitEmptyFunction: false
+
   Nested configuration flags:
 
 

include/clang/Format/Format.h

   ///
   /// If ``BreakBeforeBraces`` is set to ``BS_Custom``, use this to specify how
   /// each individual brace case should be handled. Otherwise, this is ignored.
+  /// \code{.yaml}
+  ///   # Example of usage:
+  ///   BreakBeforeBraces: Custom
+  ///   BraceWrapping:
+  ///     AfterEnum: true
+  ///     AfterStruct: false
+  ///     SplitEmptyFunction: false
+  /// \endcode
   BraceWrappingFlags BraceWrapping;
 
   /// \brief If ``true``, ternary operators will be placed after line breaks.