Add ScanCode toolkit and AboutCode tools to comparison page

[pombredanne]

That could make sense, especially since the REUSE tool is reusing AboutCode's license-expression library.
@mxmehl @carmenbianca Would a PR be fine by you? or do you prefer handling it?

Note also that I help maintain this list of tools https://wiki.debian.org/CopyrightReviewTools

[carmenbianca]

This makes sense to me. I'm surprised ScanCode wasn't on the list. If you'd like to make a PR, that'd be great.

[pombredanne]

Ack... I will do so.!