Add Coverage Status badge

README.md

@@ -1,4 +1,4 @@
-[![Build Status](https://travis-ci.org/Psiphon-Labs/psiphon-tunnel-core.png)](https://travis-ci.org/Psiphon-Labs/psiphon-tunnel-core)
+[![Build Status](https://travis-ci.org/Psiphon-Labs/psiphon-tunnel-core.png)](https://travis-ci.org/Psiphon-Labs/psiphon-tunnel-core) [![Coverage Status](https://coveralls.io/repos/github/Psiphon-Labs/psiphon-tunnel-core/badge.svg?branch=master)](https://coveralls.io/github/Psiphon-Labs/psiphon-tunnel-core?branch=master)
 
 Psiphon 3 Tunnel Core README
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