add example with genesis patch for parachain, i.e. adding assets to asset hub

[brenzi]

Is your feature request related to a problem? Please describe.

I had to reverse-engineer quite a bit to find out how to patch genesis as there are no docs about it.

Describe the solution you'd like

How about this example for asset hub?

[[parachains]]
id = 1000
addToGenesis = true
cumulus_based = true
chain = "asset-hub-rococo-local"

[parachains.genesis.runtimeGenesis.patch.balances]
balances = [
    ["5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY", 3000000000000]
]

[parachains.genesis.runtimeGenesis.patch.assets]
accounts = [
    [1984, "5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY", 30000000000000]
]
assets = [
    [
        1984,
        "1jMhfSJv5MkSQmEq97UmXCmMV63SHoQ3ednwkRSKETrCREU",
        true,
        1
    ]
]
metadata = [
    [
        1984,
        [84, 101, 116, 104, 101, 114, 32, 85, 83, 68], # "Tether USD" as ASCII array
        [85, 83, 68, 84], # "USDT" as ASCII array
        6
    ]
]

[parachains.genesis.runtimeGenesis.patch.foreignAssets]
accounts = [
    [
        { parents = 2, interior = { X2 = [{ GlobalConsensus = { Ethereum = { chain_id = 1 } } }, { AccountKey20 = { key = [160, 184, 105, 145, 198, 33, 139, 54, 193, 209, 157, 74, 46, 158, 176, 206, 54, 6, 235, 72] } }] } },
        "5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY",
        30000000000000
    ]
]
assets = [
    [# USDC on ethereum: 0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48
        { parents = 2, interior = { X2 = [{ GlobalConsensus = { Ethereum = { chain_id = 1 } } }, { AccountKey20 = { key = [160, 184, 105, 145, 198, 33, 139, 54, 193, 209, 157, 74, 46, 158, 176, 206, 54, 6, 235, 72] } }] } },
        "1jMhfSJv5MkSQmEq97UmXCmMV63SHoQ3ednwkRSKETrCREU",
        true,
        1
    ]
]

Describe alternatives you've considered

No response

Additional context

No response

[pepoviola]

Hi @brenzi, sorry about the lack of documentation related to this feature. I will add docs for patching the genesis in both relay and parachain. Also, we can include that example in the repo and linking from the documentation.
Again, sorry about the lack of docks and thanks for your feedback and contribution!

Thx!