fluidsynth: add page (#10576)

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>
Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

pages/linux/fluidsynth.md

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+# fluidsynth
+
+> Synthesize audio from MIDI files.
+> More information: <https://github.com/FluidSynth/fluidsynth/wiki/UserManual>.
+
+- Play a MIDI file:
+
+`fluidsynth --audio-driver={{pipewire|pulseaudio}} {{path/to/soundfont.sf2}} {{path/to/file.midi}}`