message: link to nodejs readme now that it exists
diff: This shows how to change the verkey that the ledger associates with
  a DID. It builds on ["Write DID and Query Its Verkey"](../write-did-and-query-verkey/README.md).
  -[ [Python](python/README.md) | [Java](java/README.md) | [.NET](../not-yet-written.md) | [Node.js](../not-yet-written.md) | [Objective C](../not-yet-written.md) | [Rust](rust/README.md) ]
  +[ [Python](python/README.md) | [Java](java/README.md) | [.NET](../not-yet-written.md) | [Node.js](nodejs/README.md) | [Objective C](../not-yet-written.md) | [Rust](rust/README.md) ]
  