add covalent info into backend API libraries

Author: davidzhangg

public/content/developers/docs/apis/backend/index.md

@@ -167,6 +167,14 @@ These libraries abstract away much of the complexity of interacting directly wit
 - [Documentation](https://services.tokenview.io/docs?type=api)
 - [GitHub](https://github.com/Tokenview)
 
+**Covalent -** **_Enriched blockchain APIs for 200+ Chains._**
+
+- [covalenthq.com](https://www.covalenthq.com/)
+- [Documentation](https://www.covalenthq.com/docs/api/)
+- [GitHub](https://github.com/covalenthq)
+- [Discord](https://www.covalenthq.com/discord/)
+
+
 ## Further reading {#further-reading}
 
 _Know of a community resource that helped you? Edit this page and add it!_