[CI] Add build status badge (#1)

Author: tqchen

README.md

@@ -17,6 +17,8 @@
 
 VTA Hardware Design Stack
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+[![Build Status](https://ci.tvm.ai/job/tvm-vta/job/master/badge/icon)](https://ci.tvm.ai/job/tvm-vta/job/master/)
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 VTA (versatile tensor accelerator) is an open-source deep learning accelerator complemented with an end-to-end TVM-based compiler stack.
 
 The key features of VTA include: