[BUG] Links in Docker docs broken

[jamesgorrie]

Context:

• Playwright Version: 1.7.1
• Operating System: All
• Node.js version: N/A
• Browser: N/A
• Extra: N/A

Describe the bug

Documentation in docker hub has become out of date with updates to this repo. They should be updated.

It seems as thought there was a time where markdown files didn't have .md extensions. It's hard to tell as the history to these files aren't easily accessible in GitHub.

[JoelEinbinder]

@pavelfeldman looks like cleanup after you moved all the docs around.

[mxschmitt]

Maybe by that it can also be added that there exists an Ubuntu 20 image.

[jamesgorrie]

Another option would be to use automated builds which would then take the README file from repo.

Not sure if that's something that would be desired though, as I am new to the repo.

[aslushnikov]

Links are working now!