Add RTTY Operation wiki page
Explains Mark/Space dashed lines on the panadapter, what they mean,
how to tune RTTY signals, default settings (2125 Hz mark, 170 Hz shift),
and how to use RTTY with external software via DAX/CAT.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>