Mention fix for lately recognized external devices in CHANGELOG
Add mailing list information

A mailing list may be a useful [neutral] channel for users that do not
have github accounts, and possibly better suited for some design
discussions.
Reformulate 'Contributing' section

It sounds less fundamentalistic now and provides some more useful
resources.
Improve usage information in README slightly
Minor changes to README
Bump version
Merge branch 'publish-0.6.4'