README: correct soundfont licensing (FluidR3 is MIT, apt-installable) + OPL3 alternative

README.md

@@ -104,7 +104,19 @@ on a peak of 32767.
 - A bar-length linter in the score parser catches more composition bugs
   than any amount of staring at note lists.
 
-## Licence
+## Licence & soundfonts
 
-MIT — see [LICENSE](LICENSE). Soundfonts are not bundled (licensing);
-install FluidR3_GM.sf2 or your favourite GM soundfont separately.
+MIT — see [LICENSE](LICENSE). Rendering needs a General MIDI soundfont,
+which is **not bundled only because of size**, not licence: FluidR3_GM.sf2
+is MIT-licensed and installs with one command —
+
+```bash
+apt install fluid-soundfont-gm   # FluidR3, 148MB, MIT — what we use
+apt install timgm6mb-soundfont   # TimGM6mb, ~6MB, lighter fallback
+```
+
+Soundfonts are sample libraries for the synth (timidity/fluidsynth) —
+MIDI files themselves contain no audio. For authentic 1993 Sound Blaster
+flavour, OPL3 emulators (ymfmidi, libADLMIDI) need no soundfont at all:
+they synthesise FM like the real card. Game engines supply their own MIDI
+synthesis, so shipped game assets never need a soundfont bundled either.