[Gimp-web] Add Bitcoin Cash or Monero donation address

[Piotr Kąkol <piotrkakol protonmail com>]

Hello.

The only cryptocurrency you can donate to Gimp devs is Bitcoin.
​Bitcoin is useless for donations in this state because of huge fees.
You can check out this fee chart comparing Bitcoin, Bitcoin Cash and Monero fees in the last 3 months:
https://bitinfocharts.com/comparison/transactionfees-btc-bch-xmr.html#3m

The average fee for BTC is over $25 at this moment. How much someone would have to want to donate to justify 
that fee?

It would be cool if you provided official Bitcoin Cash and/or Monero addresses.

Best regards,
Piotr