Readme.md: more badges

- minimum Go version
- show officially supported platforms

Change-Id: Ic5ce8a14187eb694cae4146cb116dc493c5e9336
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2300
Reviewed-by: Marcel van Lohuizen <mpvl@google.com>
diff --git a/README.md b/README.md
index adf3bac..7b785d3 100644
--- a/README.md
+++ b/README.md
@@ -16,6 +16,8 @@
 [![GoDoc](https://godoc.org/cuelang.org/go?status.svg)](https://godoc.org/cuelang.org/go)
 [![Appveyor](https://ci.appveyor.com/api/projects/status/0v3ec7p5162hpwpe?svg=true)](https://ci.appveyor.com/project/mpvl/cue)
 [![Go Report Card](https://goreportcard.com/badge/github.com/cuelang/cue)](https://goreportcard.com/report/github.com/cuelang/cue)
+[![Go 1.12](https://img.shields.io/badge/go-1.12-9cf.svg)](https://golang.org/dl/)
+[![platforms](https://img.shields.io/badge/platforms-linux|windows|macos-inactive.svg)]()
 
 
 # The CUE Data Constraint Language