Update D1 import/export with note about sqlite 3.50.0 exporting

[Friss]

Added note about sqlite v3.50.0 requirement for .dump command.

Summary

sqlite 3.50.0 uses a new unistr() command in dumps which is not supported in D1. https://sqlite.org/releaselog/3_50_0.html

So dropping a note about how to get sqlite to not output the command in its dump.

Screenshots (optional)

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