Add changelog.

CHANGELOG.rst

+Changelog
+=========
+
+`1.0a1`_
+--------
+
+New features
+~~~~~~~~~~~~
+
+* Display audit trail in lesson view
+* Add printout of register for archival purposes
+
+Bugfixes
+~~~~~~~~
+
+* Fix off-by-one error in some date headers
+* Deduplicate lessons of child groups in group week view
+* Keep selected group in group week view when browsing weeks
+* Correctly display substitutions in group week view
+* Support underfull school weeks (at start and end of timetable effectiveness)
+
+Minor changes
+~~~~~~~~~~~~~
+
+* Use bootstrap buttons everywhere
+
+_`1.0a1`: https://edugit.org/Teckids/BiscuIT/BiscuIT-App-Alsijil/-/tags/1.0a1