Add changelog.

CHANGELOG.rst

+Changelog
+=========
+
+`1.0a1`_
+--------
+
+New features
+~~~~~~~~~~~~
+
+* Deactivate persons that are set to inactive in SchILD
+
+Minor changes
+~~~~~~~~~~~~~
+
+* Use bootstrap buttons everywhere
+* Show number of created and deactivated persons after import
+
+_`1.0a1`: https://edugit.org/Teckids/BiscuIT/BiscuIT-App-SchILD-NRW/-/tags/1.0a1