docs: add RPC usage clarification note

Adds a clarification note about using the correct RPC endpoint when building on Base.

Author: erhnysr

README.md

@@ -164,3 +164,6 @@ The core team will review opened PRs. The SLA is 2 weeks, generally on a first-c
 ## Storybook for UI components
 
 See `storybook/README.md` for details on local Storybook and component docs.
+## Additional Note
+
+When building on Base, always ensure that you are using the correct RPC endpoint for the intended network (mainnet or testnet). Misconfiguration can lead to failed transactions or unexpected behavior.