[ntuple] Add boost_combine copyright and license

Author: enirolf

tree/ntuple/v7/inc/ROOT/RNTupleJoinTable.hxx

@@ -70,6 +70,42 @@ private:
       /// proposed, by [David Stafford](https://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html), [Pelle
       /// Evensen](https://mostlymangling.blogspot.com/2019/12/stronger-better-morer-moremur-better.html), and [Jon
       /// Maiga](http://jonkagstrom.com/mx3/mx3_rev2.html). We currently use Jon Maiga’s function."
+      ///
+      /// \note
+      /// \parblock
+      /// Copyright 2005-2014 Daniel James.
+      /// Copyright 2021, 2022 Peter Dimov.
+      /// Distributed under the Boost Software License, Version 1.0.
+      /// https://www.boost.org/LICENSE_1_0.txt
+      ///
+      /// Based on Peter Dimov's proposal
+      /// http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1756.pdf
+      /// issue 6.18.
+      ///
+      /// Boost Software License - Version 1.0 - August 17th, 2003
+      ///
+      /// Permission is hereby granted, free of charge, to any person or organization
+      /// obtaining a copy of the software and accompanying documentation covered by
+      /// this license (the "Software") to use, reproduce, display, distribute,
+      /// execute, and transmit the Software, and to prepare derivative works of the
+      /// Software, and to permit third-parties to whom the Software is furnished to
+      /// do so, all subject to the following:
+      ///
+      /// The copyright notices in the Software and this entire statement, including
+      /// the above license grant, this restriction and the following disclaimer,
+      /// must be included in all copies of the Software, in whole or in part, and
+      /// all derivative works of the Software, unless such copies or derivative
+      /// works are solely in the form of machine-executable object code generated by
+      /// a source language processor.
+      ///
+      /// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+      /// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+      /// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+      /// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+      /// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+      /// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+      /// DEALINGS IN THE SOFTWARE.
+      /// \endparblock
       struct RCombinedJoinFieldValueHash {
          inline std::size_t operator()(const RCombinedJoinFieldValue &joinFieldVal) const
          {