Add SPDX metadata for the Wigner Symbols source

This code was taken from:
https://github.com/joeydumont/wignerSymbols/blob/master/src/wignerSymbols-fortran.f

src/fortran/wignerSymbols.f

+C SPDX-FileCopyrightText: 1976 K. Schulten and R. G. Gordon
+C SPDX-FileCopyrightText: 2014-2015 Joey Dumont
+C SPDX-FileCopyrightText: 2018 Christopher Kerr
+C
+C SPDX-License-Identifier: LGPL-3.0-or-later
+C
 C The DRC3JJ subroutine was copied from the 'wignerSymbols' project by Joey Dumont,
 C and has been modified to make it a PURE subroutine and thus compatible with OpenMP.
 C The original version of the file can be found here: