Clarify the fields in the memory adjustment dialog

[KKoukiou]

Discussed in https://github.com/cockpit-project/cockpit-machines/discussions/270

^{Originally posted by Verhoeckx July 22, 2021} I have two question about the memory usage of virtual machines:

1. Is the memory static of dynamic?
2. Is there a general how much memory you should assign to a virtual machine?

With static I mean the host system always uses all allocated memory (even when the virtual machine uses less). With dynamic I mean the host systems only uses the memory that the virtual machine is actually using.

@KKoukiou: Do you have time to answer above questions :smiley: ?