[dsablic]

Adds one PID for SIDOU, open-source firmware for the M-VAVE FM-1 that turns it into a Commodore 64 SID instrument.

• Source: https://github.com/dsablic/sidou (LICENSE file at the root: GPL-3.0-or-later, with the firmware image as built GPL-3.0-only because it links Felucca's GPL-3.0-only USB stack; LICENSING.md has the details)
• Site: https://dsablic.github.io/sidou/
• Hardware: the unmodified, mass-produced M-VAVE FM-1; there is no custom PCB, so the firmware is the whole project.
• Why a PID of its own: SIDOU's application currently enumerates as 1209:0001, the test PID, which Felucca's firmware (the stock FM-1 community firmware whose USB stack SIDOU vendors) also uses. SIDOU is distributed, so it should not sit on the test PID. The update loader stays Felucca's, unmodified, on 1209:0002; this request is for the application image only.
• One PID requested, 0x51D0 ("SID0"), unused on 1209 at the time of the PR; not in the reserved 0xxx/1xxx ranges.
• Files: org/dsablic/index.md and 1209/51D0/index.md.