Add changelog entry for Digest Auth

Author: WhyNotHugo

CHANGELOG.rst

@@ -17,6 +17,7 @@ Version 0.19.3
 - Add an option to request vCard v4.0.  :gh:`1066`
 - Require matching ``BEGIN`` and ``END`` lines in vobjects. :gh:`1103`
 - A Docker environment for Vdirsyncer has been added `Vdirsyncer DOCKERIZED <https://github.com/Bleala/Vdirsyncer-DOCKERIZED>`_.
+- Implement digest auth. :gh:`1137`
 
 Version 0.19.2
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