Add CodeSandbox example to README (#621)

* Add CodeSandbox example to README

I found myself using CodeSandbox to test features and share examples frequently enough that I made a template for it based on the quick start guide in the README.

This adds a link to that template below the quick start section so people can jump right in to a live demo and tweak/edit it as they like.

* Include "edit" in the sandbox link

"You can [edit this example live]" instead of "You can edit [this example live]"

README.md

@@ -102,6 +102,8 @@ function getData([col, row]: Item): GridCell {
 }
 ```
 
+You can [edit this example live](https://codesandbox.io/s/glide-data-grid-template-ydvnnk) on CodeSandbox
+
 ## Full API documentation
 
 The full [API documentation is on the main site](https://grid.glideapps.com/docs/index.html).