Adds CHANGELOG.md

A changelog is added to document changes that are made to the adapter.
Information on the initial release (v0.1) is incomplete.

CHANGELOG.md

+# DuMuX-preCICE change log
+
+## Not released yet
+
+- 2022-02-10: Added `CHANGELOG.md` to track changes of the adapter.
+
+## v0.1
+
+This marks the initial release of the DuMuX-preCICE adapter.
+
+- Should represent the state of adapter used in publication [Jaust2020a](https://git.iws.uni-stuttgart.de/dumux-pub/jaust2020a).
+- Requires preCICE 1.6
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