Example code typo at /xtc/README.md

[KevinTroyT]

A commend line typo which causes bash returns an error
$ dfx canister --network=ic --wallet=$(dfx identity --network=ic get-wallet) call --with-cycles AMOUNT aanaa-xaaaa-aaaah-aaeiq-cai mint "(principal \"Some-Principal-ID\",0:nat")"
Should be
$ dfx canister --network=ic --wallet=$(dfx identity --network=ic get-wallet) call --with-cycles AMOUNT aanaa-xaaaa-aaaah-aaeiq-cai mint "(principal \"Some-Principal-ID\",0:nat)"