Update README.md

Author: aaguiarz

README.md

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 # Auth0 Golang API Samples
 
+[![CircleCI](https://img.shields.io/circleci/project/github/auth0-samples/auth0-golang-api-samples.svg?style=flat-square)](https://circleci.com/gh/auth0-samples/auth0-golang-api-samples/tree/master)
+
 These samples demonstrate how to create an API with Go which only permits access to resources if a valid **access token** is included. This verification is done by validating the signature and claims in a JSON Web Token (JWT) signed by Auth0.
 
 These samples do not demonstrate how to sign a JWT but rather assume that a user has already been authenticated by Auth0 and holds an access token for API access. For information on how to use Auth0 to authenticate users, see [the docs](https://auth0.com/docs).
@@ -30,4 +32,4 @@ If you have found a bug or if you have a feature request, please report them at
 
 ## License
 
-This project is licensed under the MIT license. See the [LICENSE](LICENSE.txt) file for more info.
+This project is licensed under the MIT license. See the [LICENSE](LICENSE.txt) file for more info.