Problem: missing ADR for precompile

[thomas-nguy]

Significant improvements has been made in Cronos to enable precompile, unlocking cosmos features (such as staking or ica) at the the EVM layer. Those changes should ideally be documented with an ADR : https://github.com/crypto-org-chain/cronos/tree/main/docs/architecture

Some key points to be documented :

• motivation
• custom changes in ethermint/ go-ethereum
• serialisation format of cosmos msgs at evm layer
• gas/response handling