Update README.md

Author: shawnps-sigsci

README.md

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+[![GoDoc][doc-img]][doc]
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 # sigsci-module-golang
 
 The Signal Sciences module in golang allows for integrating your golang
@@ -61,3 +64,6 @@ go run examples/helloworld/main.go localhost:9999
 
 This will run a HTTP listener on `localhost:8000`, which will send any
 traffic to this listener to a running sigsci-agent for inspection.
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+[doc-img]: https://godoc.org/github.com/signalsciences/sigsci-module-golang?status.svg
+[doc]: https://godoc.org/github.com/signalsciences/sigsci-module-golang