Add licence to Fluid R3 sf3

Fix for MuseScore Issue #27306 - provide licence for Fluid sf3 file
OK so I would keep the original SF2 version license. And just add in front.

```
The FluidR3 SF3 soundfont was compressed from the Fluid R3 SF2 soundfont and retains the copyright and licencing of the original and uncompressed sound font as follows:-
More info about the SF3 format and compression algorithm: https://github.com/wschweer/sftools
```