Reword development warning

Reword the warning at the start of the readme to be less intimidating,
as this is the correct version of the project that users are expected to
install.

README.md

@@ -4,18 +4,17 @@
 <br/>
 <br/>
 
-# Warning
-
-Do not use master branch to run your Clusterio - master now is a development version and may not work
-
-Use latest stable release: https://github.com/clusterio/factorioClusterio/releases/latest
-
-Or clone latest stable branch that has name format `x.y.z`
-
 # factorioClusterio
 
 Discord for development/support/play: https://discord.gg/5XuDkje
 
+## Important notice
+
+This is the stable branch of the project.  The
+[master branch][http://github.com/clusterio/factorioClusterio/tree/master]
+is undergoing significant changes that breaks compatibility to plugins and
+existing installations and is not recommended for use.
+
 ### Ways to support me/the project:
 
 * Contribute with code/documentation. Always nice to move the project forward