Added copyright file and list of people involved

src/metatensor/.gitignore

@@ -6,7 +6,7 @@
 !/*.h
 !/*.sh
 !/Makefile
-!/README
 !/README.md
 !/module.type
 !/COPYRIGHT
+!/PEOPLE-METATENSOR

src/metatensor/COPYRIGHT

@@ -0,0 +1,20 @@
+   Copyright (c) 2024 The METATENSOR code team
+   (see the PEOPLE-METATENSOR file at the root of this folder for a list of names)
+
+   See https://lab-cosmo.github.io/metatensor/latest/ for more information about the 
+   metatensor package that this module allows you to call from PLUMED.
+
+   This file is part of METATENSOR code module.
+
+   The METATENSOR code module is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   The METATENSOR code module is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with the METATENSOR code module.  If not, see <http://www.gnu.org/licenses/>.

src/metatensor/PEOPLE-METATENSOR

@@ -0,0 +1,12 @@
+METATENSOR code is covered under the GNU LESSER GENERAL PUBLIC LICENSE 
+(see COPYING.LESSER in PLUMED2 root directory).
+This license applies to all the source code in this directory, 
+except from where explicitly indicated.
+
+Authors of this software are:
+
+- Guillaume Fraux (Github: @Luthaf)
+
+The following people have contributed to this software: 
+
+- Gareth Tribello(Github: @gtribello)