doc/resampler: add exact_rational option

Signed-off-by: NMuhammad Faiz <mfcc64@gmail.com>

doc/resampler.texi

@@ -120,8 +120,8 @@ select the native SW Resampler; filter options precision and cheby are not
 applicable in this case.
 @item soxr
 select the SoX Resampler (where available); compensation, and filter options
-filter_size, phase_shift, filter_type & kaiser_beta, are not applicable in this
-case.
+filter_size, phase_shift, exact_rational, filter_type & kaiser_beta, are not
+applicable in this case.
 @end table
 
 @item filter_size
@@ -134,6 +134,11 @@ the interval [0,30].
 @item linear_interp
 Use linear interpolation if set to 1, default value is 0.
 
+@item exact_rational
+For swr only, when enabled, try to use exact phase_count based on input and
+output sample rate. However, if it is larger than @code{1 << phase_shift},
+the phase_count will be @code{1 << phase_shift} as fallback. Default is disabled.
+
 @item cutoff
 Set cutoff frequency (swr: 6dB point; soxr: 0dB point) ratio; must be a float
 value between 0 and 1.  Default value is 0.97 with swr, and 0.91 with soxr