Add link back to home page from docs (chartjs#6435)

* Add link back to home page from docs chartjs#6433

* Modify link texts

* Edit homepage link

Author: jacobsorme

docs/SUMMARY.md

@@ -1,6 +1,7 @@
 # Summary
 
-* [Chart.js](README.md)
+* [Chart.js](https://www.chartjs.org)
+* [Introduction](README.md)
 * [Getting Started](getting-started/README.md)
   * [Installation](getting-started/installation.md)
   * [Integration](getting-started/integration.md)