Added CHANGELOG

CHANGELOG.md

+# Change Log
+
+## Version ??? - Soon
+
+- Fix typos, wrong value displays
+- Reworked activity display and allow HTML display inputs
+- Allowed easy activity duplication
+- Separate activity must_subscribe display from actual subscriptions
+	(so a single activity can have multiple clones: one displayed in list, and multiple in
+	planning and inscription lists if occurs more than once)
+
+## Version 1.0.1 - day one patch - 2021-03-24
+
+- Fix missing field `is_staff` in user model
+- Fix non-nullable setting `activity_submission_form`
+
+## Version 1.0.0 - 2021-03-24
+
+- Initial release