Add "Open with Codeanywhere" badge to examples/studio/custom-datagrid…

[nkkko]

…-column/README.md

• I've read and followed the contributing guide on how to create great pull requests.
• I've updated the relevant documentation for any new or updated feature.
• I've linked relevant GitHub issue with "Closes #".
• I've added a visual demonstration in the form of a screenshot or video.

Why?

With Codeanywhere, devs and contributors can:

• Instantly launch a cloud or local IDE with remote dev environment.
• Automatically set up and configure a remote dev environments if a devcontainer.json file is present.

Benefits:

1. Faster onboarding for new contributors.
2. Consistent and ready-to-use development environments.
3. Flexibility to work in the cloud or locally.

[Janpot]

🤔 this looks like it requires me to create an account with them. And are you sure this opens the example? It looks like it opens the whole Toolpad repo.