Resolve "Release Notes 5.3"

Closes #1846

Merge request studip/studip!1217

RELEASE-NOTES.md

+# Stud.IP v *version*
+
+*Datum*
+
+## Neue Features
+
+- ...
+
+## Breaking changes
+
+- ...
+
+## Bugfixes
+
+- ...
+
+## Veraltete Features
+
+- ...