message: doc: change known issues link to project board
diff: @@ -20,7 +20,7 @@ Nervos CKB is released under the terms of the MIT license. See [COPYING](COPYING
  ## Development Process
  This project is still in development, and it's NOT in production-ready status.
  -The wiki also lists some [known issues](https://github.com/nervosnetwork/ckb/wiki/Known-Issues) that we are currently working on.
  +The wiki also lists some [known issues](https://github.com/nervosnetwork/ckb/projects/2) that we are currently working on.
  The `master` branch is regularly built and tested, however, it is not guaranteed to be completely stable; The `develop` branch is the work branch to merge new features, and it's not stable. The CHANGELOG is available in [Releases](https://github.com/nervosnetwork/ckb/releases) and [CHANGELOG.md](https://github.com/nervosnetwork/ckb/blob/master/CHANGELOG.md) in the `master` branch.
  