Update readme that bitbucket labels are supported

[jeffwidman]

25 added support for bitbucket labels/metadata/component and translates them to github labels:

https://github.com/jeffwidman/bitbucket_issue_migration/blob/master/migrate.py#L295

@nicoddemus do you remember what bitbucket metadata & component types refer to?

[nicoddemus]

Hi @jeffwidman!

IIRC my patch mapped kind and component to GH labels... does that answer your question? :smile:

[jeffwidman]

Yep thx