Update readme for static imports and export command

[el-j]

1. some little updates for the readme in point 4. to prevent getting trapped with static import ;)
2. changed the export command according to the nextjs docs

[Niels-IO]

Hi @el-j,

Thanks for the PR. I updated the README with the export commands.

For the static images though, I tested it again, and it works in my example app (that is in the example folder of the repo here) where I use a statically imported image from the public folder.