[Feature Request] possibility to add a dns server manually

[Eatery1576]

I really love this project and it has helped me out finding faster dns server based on my location. I am a big fan of your work.

Got a wish that I manually could add 1 or 2 extra dns serveres to the test list. That way I can check the speed on dns server from places like IPS, to get a comparison on improved performance.

also maybe the possibility to keep the manually added websites, like if I am doing like a test regularly.

Keep up the good work. I will keep using your project.