Update CHANGELOG

Author: tcompa

CHANGELOG.md

@@ -0,0 +1,10 @@
+*Note: Numbers like (\#123) point to closed Pull Requests on the fractal-web repository.*
+
+# 0.5.2
+
+* Improve tasks handling within the client (\#233).
+* Prevent accidental loss of user-provided WorkflowTask arguments (\#234).
+
+# 0.5.1
+
+First release included in this CHANGELOG.