add badge

Author: doerners

README.md

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 [![Render and deploy Bibliometrics Quick Notes to Github Pages](https://github.com/bibliometrics-quick-notes/bibliometrics-quick-notes.github.io/actions/workflows/build-quick-notes.yaml/badge.svg)](https://github.com/bibliometrics-quick-notes/bibliometrics-quick-notes.github.io/actions/workflows/build-quick-notes.yaml)
 
+[![License: CC BY 4.0](https://img.shields.io/badge/License-CC_BY_4.0-lightgrey.svg)](https://creativecommons.org/licenses/by/4.0/)
+
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 This repository contains the source of the [Bibliometrics Quick Notes](https://bibliometrics-quick-notes.github.io/).