Add warning for safe 7702 upgrades (coinbase#156)

* add warning not to 7702-delegate directly to CBSW impl

* update text for gh style warning

* match katzman's

Author: amiecorso

README.md

@@ -78,6 +78,14 @@ Today, allowed are
 - MultiOwnable.removeOwnerAtIndex
 - UUPSUpgradeable.upgradeToAndCall
 
+> [!WARNING]
+> ## EIP-7702 delegation safety
+> Do **not** directly delegate to a Coinbase Smart Wallet **implementation** contract via EIP-7702. Delegating directly to an implementation can create a security vulnerability.
+> 
+> Instead:
+> - Use the `EIP7702Proxy` pattern: [base/eip-7702-proxy](https://github.com/base/eip-7702-proxy)
+> - See Coinbase Developer Platform docs for further guidance and an example of performing a safe EIP-7702 upgrade: [EIP-7702 FAQs – safe upgrade](https://docs.cdp.coinbase.com/paymaster/need-to-knows/eip-7702-faqs#how-do-i-upgrade-my-wallet-to-7702)
+
 ## Deployments
 Factory and implementation are deployed via [Safe Singleton Factory](https://github.com/safe-global/safe-singleton-factory), which today will give the same address across 248 chains. See "Deploying" below for instructions on how to deploy to new chains. 
 | Version   | Factory Address                        |