Update README.md

README.md

@@ -430,7 +430,7 @@ We are currently in the process of creating a pre-print to describe our methods,
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-CC-BY-4.0 (license used for Materials Project, Alexandria, OQMD) requires proper acknowledgement. 
+[CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/) (license used for Materials Project, Alexandria, OQMD) requires proper acknowledgement. 
 
 Thus, if you use materials data which include (”mp-”) in the immutable_id, please cite the [Materials Project](https://pubs.aip.org/aip/apm/article/1/1/011002/119685/Commentary-The-Materials-Project-A-materials).