docs(readme): Add Greta Lighthouse to list of Integrations (#4031)

* Add Greta Lighthouse to list of Integrations

* Update readme.md

Update text after comments.

readme.md

@@ -240,6 +240,8 @@ This section details projects that have integrated Lighthouse. If you're working
 
 * **[Calibre](https://calibreapp.com)** - Calibre is a web performance monitoring tool running Lighthouse continuously or on-demand via an API. Test using emulated devices and connection speeds from a number of geographical locations. Set budgets and improve performance with actionable guidelines. Calibre comes with a free 14-day trial.
 
+* **[Greta Lighthouse](https://lighthouse.greta.io/)** - Greta Lighthouse is a tool that lets you run free Lighthouse tests from anywhere in the world. It provides insights into your users' perceived performance and recommendations on how to improve. The tool considers parameters such as location and type of device to simulate real user conditions. [Greta](https://greta.io/) also provides a new type of platform that helps companies understand, control, and improve their users’ experience via an innovative approach to content delivery.
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 * **[HTTPArchive](http://httparchive.org/)** - HTTPArchive tracks how the web is built by crawling 500k pages with Web Page Test, including Lighthouse results, and stores the information in BigQuery where it is [publicly available](https://discuss.httparchive.org/t/quickstart-guide-to-exploring-the-http-archive/682).
 
 * **[Treo](https://treo.sh)** - Treo is Lighthouse as a Service. It provides regression testing, geographical regions, custom networks, and integrations with GitHub & Slack. Treo is a paid product with plans for solo-developers and teams.