docs(errors/large-page-data): how to see data being passed to page

[ryparker]

Summary

This PR adds a note about how to see the data that this error is complaining about:

Warning: data for page "/" is xxx which exceeds the threshold of 128 kB, this amount of data can reduce performance.

This debug trick was something I came across in a discussion and I thought it would be helpful to others like it was for me.

Documentation / Examples

• Make sure the linting passes by running pnpm lint
• The examples guidelines are followed from our contributing doc

[ijjk]

Thanks!