adding one sentence regarding the lowpass filter (#9089)

* adding one sentence regarding the lowpass filter

* adding one sentence regarding the lowpass filter, fixed line length

* Update mne/io/meas_info.py

Co-authored-by: Eric Larson <[email protected]>

* Update mne/io/meas_info.py

Co-authored-by: Eric Larson <[email protected]>

Co-authored-by: Eric Larson <[email protected]>

Author: ChristinaZhao

mne/io/meas_info.py

@@ -284,6 +284,8 @@ class Info(dict, MontageMixin):
         Tilt angle of the gantry in degrees.
     lowpass : float
         Lowpass corner frequency in Hertz.
+        It is automatically set to half the sampling rate if there is
+        otherwise no low-pass applied to the data.
     meas_date : datetime
         The time (UTC) of the recording.