README: add --softinv

demod/mod/README.md

@@ -64,6 +64,6 @@ alternative decoders using cross-correlation for better header-synchronization
   soft input:<br />
   Option `--softin` expects float32 symbols as input, with `s>0` corresponding to `bit=1`.<br />
   (remark/caution: often soft bits are defined as `bit=0 -> s=+1` and `bit=1 -> s=-1` such that the identity element `0`
-  for addition mod 2 corresponds to the identity element `+1` for multiplication.)
-
+  for addition mod 2 corresponds to the identity element `+1` for multiplication.)<br />
+  There is also the option `--softinv` for input with `s<0` corresponding to `bit=1` (e.g. `fsk_demod`).