Merge pull request #1244 from sarven/master

Add a link to Unit Testing Tips

README.md

 * [PHP Watch](https://php.watch/) - PHP articles, news, upcoming changes, RFCs and more.
 * [PHP Weekly](https://www.phpweekly.com/archive.html) - A weekly PHP newsletter.
 * [Seven PHP](https://7php.com/) - A website that interviews members of the PHP community.
+* [Unit Testing Tips](https://testing-tips.sarvendev.com/) - Unit Testing Tips by examples in PHP.
 
 ### PHP Books
 *Fantastic PHP-related books.*