Add Kurtosis to list of testing tools (#1063)

* Add Kurtosis to list of testing tools

Hey team! We'd like to add Kurtosis to the list of testing tools. 

*What is Kurtosis?* Kurtosis is a built system for multi-(docker)container test environments. 
*What is Kurtosis for?* Kurtosis is for engineers who dev against large distributed systems/applications and who experience pain when trying to configure multi (Docker) container environments for their testing workflows. 

Kurtosis can be used locally without the need to sign up and is free-forever under a source-available license (BSL). 

We have:
- Linked out to our Github: https://github.com/kurtosis-tech/kurtosis
- [A README on our GIthub](https://github.com/kurtosis-tech/kurtosis#readme)
- Content about how to setup/install the project (in our [Github README](https://github.com/kurtosis-tech/kurtosis#to-start-using-kurtosis) and on our [docs](https://docs.kurtosis.com/install)),
- Lots of great examples on: [Github](https://github.com/kurtosis-tech/awesome-kurtosis#awesome-kurtosis-) and in our [docs](https://docs.kurtosis.com/). 

I followed the [Quality Standards](https://github.com/veggiemonk/awesome-docker/blob/master/.github/CONTRIBUTING.md#quality-standards) you guys wrote, but please let me know if you've got any questions about Kurtosis or if we missed something!

Thanks

* add "composable" to description

README.md

@@ -669,6 +669,7 @@ Services to securely store your Docker images.
 -   [DockerSpec](https://github.com/zuazo/dockerspec) - A small Ruby Gem to run RSpec and Serverspec, Infrataster and Capybara tests against Dockerfiles or Docker images easily. By [@zuazo](https://github.com/zuazo)
 -   [Dockunit](https://github.com/dockunit/platform) :skull: - Docker based integration tests. A simple Node based utility for running Docker based unit tests. By [@dockunit](https://github.com/dockunit)
 -   [InSpec][inspec] - InSpec is an open-source testing framework for infrastructure with a human- and machine-readable language for specifying compliance, security and policy requirements. By [@chef](https://github.com/chef)
+-   [Kurtosis](https://github.com/kurtosis-tech/kurtosis) - A composable build system for multi-container test environments that provides developers with: a powerful Python-like SDK for environment configuration, a compile-time validator to verify environment behavior & setup, and a runtime for environment execution, monitoring, & debugging capabilities. By [Kurtosis](https://www.kurtosis.com/)
 -   [Pull Dog](https://github.com/apps/pull-dog) - A GitHub app that automatically creates Docker-based test environments for your pull requests, from your docker-compose files. Not open source.
 -   [Pumba](https://github.com/alexei-led/pumba) - Chaos testing tool for Docker. Can be deployed on kubernetes and CoreOS cluster. By [@alexei-led](https://github.com/alexei-led)