Add docs on using gas.zip for Flame

[jbowen93]

https://www.gas.zip/

Gas address on Flame: https://explorer.flame.astria.org/address/0x8C826F795466E39acbfF1BB4eEeB759609377ba1

Test tx: https://explorer.flame.astria.org/tx/0xa51b3d052eced8508d5db83d7d925d0b62bf045afba4b487061cf8af4945a153