clarify that iolang is not yet suitable to be a dependency

README.md

@@ -1,8 +1,10 @@
 # iolang
 
+[![stability-experimental](https://img.shields.io/badge/stability-experimental-orange.svg)](https://github.com/emersion/stability-badges#experimental) [![GoDoc](https://godoc.org/github.com/zephyrtronium/iolang?status.svg)](https://godoc.org/github.com/zephyrtronium/iolang) ![Tests](https://github.com/zephyrtronium/iolang/workflows/Tests/badge.svg)
+
 This is a pure Go implementation of [Io](http://iolanguage.org/). Much of the hard work has been done, but hard work still remains.
 
-To embed an iolang interpreter into a Go program, one would use the `NewVM()` function to get a `*VM`, use `SetSlot()` to make available any extras, then feed the VM code to evaluate with its `DoString()` and `DoReader()` methods. The VM also has methods like `NewNumber()`, `NewString()`, `NewObject()`, &c. to create primitives. The API is currently incomplete and may change.
+To embed an iolang interpreter into a Go program, one would use the `NewVM()` function to get a `*VM`, use `SetSlot()` to make available any extras, then feed the VM code to evaluate with its `DoString()` and `DoReader()` methods. The VM also has methods like `NewNumber()`, `NewString()`, `NewObject()`, &c. to create primitives. The API is currently incomplete and will change.
 
 The `cmd/io` directory contains a REPL as an example of embedding iolang.