Removed direct link to issue tracker in the README - it makes it too
easy to use it for a question - and it's abused multiple times a day
for questions. It's easy enough to find it if there's a real issue
to report.

Added sentence to point people at golang-nuts and the new forum.

Change-Id: If75bab888cda064aceeefc49ef672fbb964f8f54
Reviewed-on: https://go-review.googlesource.com/15284Reviewed-by: Jason Buberel <jbuberel@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>