Update README.md with --oauth now required

[Houska1]

As per bug reports, OAuth authentication is now required. As a stop-gap, expand user instructions to explain its use, even though if Evernote policy requiring it continues, probably OAuth should become default.

[slash5toaster]

This should also be added to the help text
--oauth is not in the help text but in the readme

Usage: evernote-backup [OPTIONS] COMMAND [ARGS]...

  Evernote backup & export

  On the first run, to export notes:
  evernote-backup init-db
  evernote-backup sync
  evernote-backup export output_dir/

Options:
  Verbosity: [mutually_exclusive]
    -q, --quiet                   Quiet mode, output only critical errors.
    -v, --verbose                 Verbose mode, output debug information.
  --version                       Show the version and exit.
  --help                          Show this message and exit.

Commands:
  init-db  Initialize storage & log in to Evernote.
  sync     Sync local database with Evernote, downloading all notes.
  export   Export all notes from local database into ENEX files.
  reauth   Refresh login to Evernote, run when token expires.

[triuzzi]

@Houska1 could you please add the same to the help text? 🙏

[Houska1]

@triuzzi Apologies, I've never used the click package, and I'm currently on a laptop with no python devel environment. So unclear why the help text for oauth is not being displayed.