Update documentation and HTTP error reporting

[LawrenceWarren]

Motivation

• Following on from the merging of #7, I thought it was worthwhile to update the README.md content to mention this feature.
• I also found from my usage that the dump of a stack-trace on hitting a HTTP error was not useful. I have tidied this error up to be more legible.

  Changes

• Update documentation to mention --token flag.
• Tidy up README.md content generally.
• Stop HTTP errors from printing a stack-trace to terminal.
• Print a clear HTTP error code & message.

[chan-vince]

@LawrenceWarren thanks!