docs: Add release badge (#60)

Signed-off-by: Daniel Pacak <[email protected]>

README.md

@@ -1,12 +1,8 @@
-[![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://opensource.org/licenses/Apache-2.0)
+[![GitHub release][release-img]][release]
+[![License][license-img]][license]
 [![Coverage Status][cov-img]][cov]
 [![Build Status][ci-img]][ci]
 
-[cov-img]: https://codecov.io/github/aquasecurity/docker-bench/branch/master/graph/badge.svg
-[cov]: https://codecov.io/github/aquasecurity/docker-bench
-[ci-img]: https://travis-ci.com/aquasecurity/docker-bench.svg?branch=master
-[ci]: https://travis-ci.com/aquasecurity/docker-bench
-
 Docker-bench is a Go application that checks whether Docker is deployed securely by running the checks documented in the [CIS Docker Benchmark](https://www.cisecurity.org/benchmark/docker/).
 
 Tests are configured with YAML files, making this tool easy to update as test specifications evolve. 
@@ -41,8 +37,8 @@ go build -o docker-bench .
 ```
 
 # Tests
-Tests are specified in definition files `cfg/<version>/definitions.yaml.
-Where `<version>` is the version of docker for which the test applies.
+Tests are specified in definition files `cfg/<version>/definitions.yaml`,
+where `<version>` is the version of docker for which the test applies.
 
 # Contributing
 We welcome PRs and issue reports. 
@@ -51,3 +47,12 @@ Please include a comment with the results before and after your change.
 Your PR is more likely to be accepted if it includes tests. (We have not historically been very strict about tests, but we would like to improve this!).
 You're welcome to submit a draft PR if you would like early feedback on an idea or an approach.
 Happy coding!
+
+[cov-img]: https://codecov.io/github/aquasecurity/docker-bench/branch/master/graph/badge.svg
+[cov]: https://codecov.io/github/aquasecurity/docker-bench
+[ci-img]: https://travis-ci.com/aquasecurity/docker-bench.svg?branch=master
+[ci]: https://travis-ci.com/aquasecurity/docker-bench
+[license-img]: https://img.shields.io/badge/License-Apache%202.0-blue.svg
+[license]: https://opensource.org/licenses/Apache-2.0
+[release-img]: https://img.shields.io/github/release/aquasecurity/docker-bench.svg
+[release]: https://github.com/aquasecurity/docker-bench/releases