project: Add CircleCi badge to README.

Author: microbit-carlos

README.md

@@ -1,5 +1,7 @@
 # micro:bit MicroPython Filesystem
 
+[![CircleCI](https://circleci.com/gh/microbit-foundation/microbit-fs.svg?style=svg)](https://circleci.com/gh/microbit-foundation/microbit-fs)
+
 A TypeScript library to manipulate the micro:bit MicroPython filesystem.
 
 <img width="50%" alt="microbit-fs logo" src="https://user-images.githubusercontent.com/29712657/53014294-fb95e700-343f-11e9-856e-d70af8870c0c.png">
@@ -10,7 +12,6 @@ filesystem within a hex file is supported.
 Raw draft of the docs can be found in
 [https://microbit-foundation.github.io/microbit-fs/](https://microbit-foundation.github.io/microbit-fs/).
 
-
 ## License
 
 This software is under the MIT open source license.