Removed obsolete note stating that Akka.Cluster is prerelease, and removed -pre flag in package installation command
Removed obsolete note stating that Akka.Cluster is prerelease, and removed -pre flag in package installation command

sean-gilliam/getakka.net,akkadotnet/getakka.net,akkadotnet/getakka.net,sean-gilliam/getakka.net