docs: increase diskspace from 50 to 60?

[johanneslarsson]

The current disk usage after downloading all required game files are:

48.21 GiB

Add a few mods and start the running the server you'll quickly hit that upper limit of 50 GiB.

[jedwards-jagex]

The 50GB in the docs is a minimum for running a vanilla CS2 server. We may want to add something about modding and increased storage requirements.