Typescript support section: mention server_renderer_extensions

[ostrgard]

Recommend setting the server_renderer_extensions config option in the Typescript support section.

I experienced issues with changes to tsx and ts files not being properly updated in development. After loads of research on various levels of setup, I ran into this issue, which thankfully had a fix (I felt equally stupid as the author). I'd say typescript support is incomplete without the server_renderer_extensions config. Anything else delivers a subpar development experience.

I hope you sill consider my addition to the README, and thanks for all the work you put into this lib 👍

[BookOfGreg]

In the docs you present it as a recommendation, I appreciate that as the user always has choice.
Thank you for the contribution!