update changelog for 0.3.0 final

CHANGELOG.rst

 Change Log
 ==========
 
+
+0.3.0: 12/04/2021
+-----------------
+
+* version to use zoccalo on BM23
+* core:
+    * several minor fix (see !38)
+    * add noise operation
+    * starting saving some plot as results
+    * use h5py 3 instead of 2
+
 0.2.0: 13/08/2019
 -----------------