Add instructions on how to prune with GUI

[erciccione]

https://monero.stackexchange.com/questions/11454/how-do-i-utilize-blockchain-pruning-in-the-gui-monero-wallet-gui

[ITwrx]

if it were me, i would probably just add:

when setting up your wallet, choose to "manually manage the daemon" (i can't remember exact terminology used in the setup wizard) and add "--prune-blockchain" to the daemon flags input, then start the daemon up.

to the FAQ. I probably wouldn't bother with that whole stackexchange explanation for CLI stuff.

[erciccione]

Yeah i agree that's not necessary. A short line like the one you suggested would be enough.