docs(genesis): add documentation genesis_txs.jsonl file

[MikaelVallenet]

This PR is made since in the past i created a tool for samourai zenao project to generate txs file from a SQL database state and struggled to find informations about how to generate a genesis_txs.jsonl from scratch.

I thought it was a "unique" case but then a student from the student programs asked how to do the same.
I explained him, but i thought it would be nice to add some documentation on the format and how to create a genesis_txs.jsonl file.

My generator of genesis_txs file for zenao: https://github.com/samouraiworld/zenao/blob/03b5ef5f39e2a2cf987c4eacea6b6f3cd10a0b2a/backend/gzchain/gentxs.go

[Gno2D2]

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[Davphla]

You can use embedmd to extract the code
Example: https://github.com/gnolang/gno/blob/master/docs/builders/example-minisocial-dapp.md?plain=1

[Davphla]

nitpick: There's multiple lines in the following example.
It would be better to have like:

The file contains an array of TxWithMetadata object:

[Davphla]

I think move this above the example

[Davphla]

Some nitpicks, but LGTM!
I didn't retry the script but it looks correct to me.