Update the README to clarify pre-release status

Author: avh4

README.md

@@ -5,6 +5,8 @@
 # elm-format
 
 > `elm-format` is still in alpha.  If you run into any problems, please [report them](https://github.com/avh4/elm-format/issues).
+>
+> **The format produced by elm-format may change significantly before the 1.0.0 release.**  If this will cause problems for you, please refrain from using elm-format during the alpha- and beta-test periods.
 
 `elm-format` formats [Elm](http://elm-lang.org) source code according to a standard set of rules. It is inspired by the popular [gofmt](https://blog.golang.org/go-fmt-your-code).
 
@@ -28,7 +30,11 @@ elm-format --help  # See other command line options
 
 ## Installation [![(latest version: 0.3.0-alpha)](https://img.shields.io/badge/version-0.3.0--alpha-blue.svg)](https://github.com/avh4/elm-format/releases/tag/0.3.0-alpha)
 
-`elm-format` is still in alpha.  You will need to download the version appropriate for your OS, unzip it, and place `elm-format` or `elm-format.exe` (windows) on your `PATH`.
+> `elm-format` is still in alpha.  If you run into any problems, please [report them](https://github.com/avh4/elm-format/issues).
+>
+> **The format produced by elm-format may change significantly before the 1.0.0 release.**  If this will cause problems for you, please refrain from using elm-format during the alpha- and beta-test periods.
+
+You will need to download the version appropriate for your OS, unzip it, and place `elm-format` or `elm-format.exe` (windows) on your `PATH`.  Simpler installation options will be available once there is a stable release of elm-format.
 
 If the binary does not work for you, please [report details about your OS](https://github.com/avh4/elm-format/issues/new), or try [building from source](#building-from-source).