Documenting how to make Medley's window or text bigger

[pamoroso]

Some new users with large screens ask how to make the window or text of Medley bigger, see for example here and here.

Since this may be a FAQ it would help to document how to do this such as the --geometry and --screensize options of medley and the -pixelscale option of Maiko.

[MarceColl]

It would also be nice to tell about the draw buffer limitation, since there is an upper limit on how big the screen can be due to limitations in the VM.