- Add links at the top of the Import and Export tabs to a knowledge base
   article with information about using these features for various workflows.

 - Use a `<label>` for the "Select Hypothesis export file", since it is
   logically a label. This label is associated to the file input via `htmlFor`,
   but note the custom file input will still read the fixed button text ("Select
   a file")

 - Make labels bold in Import / Export tab to make them stand out against the
   help text, and also for consistency with the "Share" tab

Part of https://github.com/hypothesis/client/issues/5783