readme: emphasize issue tracker is for bugs/proposals

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>

README.md

@@ -12,14 +12,12 @@ in your web browser.
 Our canonical Git repository is located at https://go.googlesource.com/go.
 There is a mirror of the repository at https://github.com/golang/go.
 
-Please report issues here: https://golang.org/issue/new
-
 Go is the work of hundreds of contributors. We appreciate your help!
 
 To contribute, please read the contribution guidelines:
 	https://golang.org/doc/contribute.html
 
-##### Please note that we do not use pull requests.
+##### Note that we do not accept pull requests and that we use the issue tracker for bug reports and proposals only. Please ask questions on https://forum.golangbridge.org or https://groups.google.com/forum/#!forum/golang-nuts.
 
 Unless otherwise noted, the Go source files are distributed
 under the BSD-style license found in the LICENSE file.