Excavator: Add autorelease-bot badge to README

Author: svc-excavator-bot

README.md

@@ -1,3 +1,7 @@
+<p align="right">
+<a href="https://autorelease.general.dmz.palantir.tech/palantir/blueprint"><img src="https://img.shields.io/badge/Perform%20an-Autorelease-success.svg" alt="Autorelease"></a>
+</p>
+
 <img height="204" src="https://cloud.githubusercontent.com/assets/464822/20228152/d3f36dc2-a804-11e6-80ff-51ada2d13ea7.png">
 
 # [Blueprint](http://blueprintjs.com/) [![CircleCI](https://circleci.com/gh/palantir/blueprint/tree/develop.svg?style=svg)](https://circleci.com/gh/palantir/workflows/blueprint)