Add Speedrank (thedaviddias#307)

- [x] Check the commit's or even all commits' message styles matches our requested structure.
- [x] Check your code additions will fail neither code linting checks nor unit test.

#### Short description of what this resolves:

[Speedrank](https://speedrank.app) monitors the performance of your website in the background. It displays Lighthouse reports in time and delivers recommendations for improvement. Speedrank is a paid product with 14-day-trial.

#### Proposed changes:

- Add Speedrank to the list of performance testing tools.

👍 Thank you!

README.md

@@ -599,6 +599,7 @@ Minimum required xml markup for the `browserconfig.xml` file is as follows:
 > * 🛠 [Test your mobile speed with Google](https://testmysite.withgoogle.com)
 > * 🛠 [WebPagetest - Website Performance and Optimization Test](https://www.webpagetest.org/)
 > * 🛠 [GTmetrix - Website speed and performance optimization](https://gtmetrix.com/)
+> * 🛠 [Speedrank - Improve the performance of your website](https://speedrank.app/)
 
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