docs: restore replaygain option for ffmpeg backend
@@ -89,6 +89,10 @@ configuration file. The available options are:
Default: ``no``.
- **targetlevel**: A number of decibels for the target loudness level.
Default: 89.
+- **r128**: A space separated list of formats that will use ``R128_`` tags with
+ integer values instead of the common ``REPLAYGAIN_`` tags with floating point
+ values. Requires the "ffmpeg" backend.
+ Default: ``Opus``.
These options only work with the "command" backend:
