Update CHANGELOG.md to include Gaussian and Brickwall frequency filter features

Author: PierreRaybaut

CHANGELOG.md

@@ -7,7 +7,15 @@ See DataLab [roadmap page](https://datalab-platform.com/en/contributing/roadmap.
 
 💥 New features and enhancements:
 
-*
+* New image processing features:
+  * Added new "Gaussian frequency filter" feature:
+    * This feature allows to filter an image in the frequency domain using a Gaussian filter.
+    * It is implemented in the `sigima.proc.image.freq_fft` function.
+
+* New signal processing features:
+  * Added "Brickwall frequency filter" feature:
+    * This feature allows to filter a signal in the frequency domain using a brickwall filter.
+    * It is implemented in the `sigima.proc.signal.freq_fft` function, among the other frequency domain filtering features that were already available (e.g., `Bessel`, `Butterworth`, etc.).
 
 ## sigima 0.2.0 ##