Revise supported architectures in README

Updated README to reflect supported architectures.

Author: hardillb

README.md

@@ -5,7 +5,7 @@
 [![DockerHub Pull](https://img.shields.io/docker/pulls/nodered/node-red.svg)](https://hub.docker.com/r/nodered/node-red/)
 [![DockerHub Stars](https://img.shields.io/docker/stars/nodered/node-red.svg?maxAge=2592000)](https://hub.docker.com/r/nodered/node-red/)
 
-This project describes some of the many ways Node-RED can be run under Docker and has support for multiple architectures (amd64, arm32v6, arm32v7, arm64v8, i386 and s390x).
+This project describes some of the many ways Node-RED can be run under Docker and has support for multiple architectures (amd64 and arm64v8).
 Some basic familiarity with Docker and the [Docker Command Line](https://docs.docker.com/engine/reference/commandline/cli/) is assumed.
 
 **Note**: In version 1.2 we removed the named VOLUME from the build. It should not affect many users - but the details are [here](volumechanges.md).