Update README with otr community website and bugtracker

As it's listed in README at the moment is that bug reports are best send to an e-mail address. Currently, we have a great bugtracker for this with an cypherpunks account that anyone could login to.

We should modify the README so..:

List that bug reports are best placed onto the bugtracker.
Remove that bugreports are best send to the otr-dev mailinglist.
..?

(from redmine: created on 2014-10-11)

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