Documentation Request: Clarify supported chains and network assumptions in OnchainKit

## Overview
OnchainKit supports Base and other EVM-compatible networks, but the documentation does not clearly state which chains are officially supported. As a result, developers may not know whether examples and components are intended to work across all EVM networks.

Without an explicit list of supported chains, developers may assume full compatibility and encounter unexpected behavior on unsupported networks. This uncertainty leads to unnecessary debugging and incorrect network assumptions.

## Proposed Solution
Add a short documentation section that clearly lists supported chains and explains any network-specific assumptions or limitations.