Update CHANGELOG

It will have to be updated again with the new auto-CoR class

CHANGELOG.md

 # Change Log
 
+## 2020.4.0
+
+This is a version adds a number of features.
+
+### Application
+
+  - Automatic center of rotation estimation, working for both half-acquisition and regular scans
+  - Command line tool for splitting a NXTomo file by "z" series
+  - Volume histogram. Command line tool for merging histogram of multiple volumes.
+  - Enable to perform flat-field normalization with darks/flats from another dataset
+  - Sinogram normalization (baseline subtraction)
+  - Nabu does not need `tomwer_processes.h5` to get the "final" darks/refs anymore.
+
+### Library
+
+  - Add `misc.histogram` for computing partial histograms and merging them
+  - Add `preproc.sinogram.SinoNormalization`
+
 ## 2020.3.0
 
 This is a release for ESRF User Service Mode restart.