add PR requirements

CONTRIBUTING.md

@@ -44,6 +44,11 @@ PRs are always welcome and can be a quick way to get your fix or improvement sla
 
 For changes that address core functionality or would require breaking changes (e.g. a major release), it's best to open an Issue to discuss your proposal first. This is not required but can save time creating and reviewing changes.
 
+Before being merged into `main`/`master`, PRs that touch any solidity files MUST include:
+1. 100% test coverage.
+2. Singleton deployment to all supported networks (if the resulting bytecode changes).
+3. An audit from a reputable auditor (if any security relevant solidity code changes).
+
 In general, we follow the ["fork-and-pull" Git workflow](https://github.com/susam/gitpr)
 
 1. Fork the repository to your own Github account