Update README.md

Signed-off-by: David Rotermund <54365609+davrot@users.noreply.github.com>

scipy.signal_butterworth/README.md

@@ -4,3 +4,38 @@
 Sometimes we need to remove of frequency range from a time series. For this we can use a Butterworth filter [scipy.signal.butter](https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.butter.html) and the [scipy.signal.filtfilt](https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.filtfilt.html) command. 
 
 Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
+
+| | |
+| ------------- |:-------------:|
+| [scipy.signal.filtfilt](https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.filtfilt.html) | Apply a digital filter forward and backward to a signal. |
+| [scipy.signal.butter](https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.butter.html)  | Butterworth digital and analog filter design. |
+
+## Example data 
+
+```python
+import numpy as np
+import matplotlib.pyplot as plt
+
+samples_per_second: int = 1000
+dt: float = 1.0 / samples_per_second
+
+# 10 secs
+t: np.ndarray = np.arange(0, int(10 * samples_per_second)) * dt
+
+f_low = 1  # Hz
+f_mid = 10  # Hz
+f_high = 100  # Hz
+
+sin_low = np.sin(2 * np.pi * t * f_low)
+sin_mid = np.sin(2 * np.pi * t * f_mid)
+sin_high = np.sin(2 * np.pi * t * f_high)
+
+plt.figure(1)
+plt.plot(t, sin_low)
+plt.plot(t, sin_mid + 3)
+plt.plot(t, sin_high + 6)
+plt.xlabel("Time [s]")
+plt.ylabel("Waveform shifted")
+plt.title("unfiltered data")
+plt.show()
+```