Add initial release notes

Author: Dimitar Tasev

documentation/release-notes/21-1-1.md

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+# Release notes (ISIS Autoreduction v21.1.1)
+
+## Headlines
+Interactive plotting
+
+
+### Interactive plotting
+The webapp can now show Plotly plots that have been saved with `to_json`.
+This works similar to the static plots, but the file should end in `.json` rather than an image format.
+To get one to show in the webapp simply save out the `.json` in the `output_dir` during the reduction.