Merge pull request #1023 from Xanewok/nightly-shields

Add rust-toolstate shields to README.md

Author: nrc

README.md

@@ -1,4 +1,6 @@
 [![Build Status](https://travis-ci.org/rust-lang-nursery/rls.svg?branch=master)](https://travis-ci.org/rust-lang-nursery/rls) [![Build status](https://ci.appveyor.com/api/projects/status/cxfejvsqnnc1oygs?svg=true)](https://ci.appveyor.com/project/jonathandturner/rls-x6grn)
+[![Nightly status](https://img.shields.io/badge/dynamic/json.svg?label=rls-preview%20(Windows)&url=https%3A%2F%2Fraw.githubusercontent.com%2Frust-lang-nursery%2Frust-toolstate%2Fmaster%2F_data%2Flatest.json&query=%24%5B%3F(%40.tool%3D%3D%22rls%22)%5D.windows&colorB=lightgrey)](https://rust-lang-nursery.github.io/rust-toolstate/)
+[![Nightly status](https://img.shields.io/badge/dynamic/json.svg?label=rls-preview%20(Linux)&url=https%3A%2F%2Fraw.githubusercontent.com%2Frust-lang-nursery%2Frust-toolstate%2Fmaster%2F_data%2Flatest.json&query=%24%5B%3F(%40.tool%3D%3D%22rls%22)%5D.linux&colorB=lightgrey)](https://rust-lang-nursery.github.io/rust-toolstate/)