[Feature] Setting notes/descriptions for an instance

[justeraseme]

for multimc parity
this shouldn't need a global variant because i can't think of a scenario where you would want a default description for all instances

if this is considered, i'd love to have it in the empty space below the instance launch/edit controls like ATLauncher (which puts the description below the name but above the controls), where it's easily readable. it would be nicer than prism/multimc which uses a dedicated tab in the edit menu... not the most accessible place to check.

not sure if there was plans to put something else here, but either the log view (ehh) or some settable instance notes would be nice here. this space should really be filled, notes might be a great thing to put here
worst case scenario, a "notes" tab beside log will do

there might also need to be handling in the future for multimc importing. perhaps read from mmc's notes (however it's set... likely in the instance.json equivelent) and just apply it how quantum set it?