swarm/readme: add link to code review guidelines

swarm/README.md

@@ -39,6 +39,7 @@ Please make sure your contributions adhere to our coding guidelines:
  * Code must adhere to the official Go [formatting](https://golang.org/doc/effective_go.html#formatting) guidelines (i.e. uses [gofmt](https://golang.org/cmd/gofmt/)).
  * Code must be documented adhering to the official Go [commentary](https://golang.org/doc/effective_go.html#commentary) guidelines.
  * Pull requests need to be based on and opened against the `master` branch.
+ * [Code review guidelines](https://github.com/ethereum/go-ethereum/wiki/Code-Review-Guidelines).
  * Commit messages should be prefixed with the package(s) they modify.
    * E.g. "swarm/fuse: ignore default manifest entry"