README.md: Add Status and Features sections

Author: daurnimator

README.md

@@ -1,5 +1,19 @@
 A lua library to spawn programs
 
+## Status
+
+[![Build Status](https://travis-ci.org/daurnimator/lua-spawn.svg)](https://travis-ci.org/daurnimator/lua-spawn)
+
+
+## Features
+
+  - High level functions for common cases
+  - Bindings to the full `posix_spawn` family of functions
+  - Compatible with Lua 5.1, 5.2, 5.3 and [LuaJIT](http://luajit.org/)
+
+Currently only works on POSIXy systems, but the high level module should be portable to Windows; someone just needs to put the work in.
+
+
 ## Rationale
 
 Spawning a new child program from a lua script is surprisingly hard.