docs: add info about cube

Author: dangreen

README.md

@@ -83,6 +83,10 @@ new BarChart('#chart', {
 
 <br />
 
+Need an API to fetch data? Consider [Cube](https://cube.dev/?ref=eco-chartist), an open-source API for data apps.
+
+<br />
+
 [![supported by Cube](https://user-images.githubusercontent.com/986756/154330861-d79ab8ec-aacb-4af8-9e17-1b28f1eccb01.svg)](https://cube.dev/?ref=eco-chartist)
 
 ## What is it made for?