Update Code Monitors' getting started page information box copy and add box to creation page.

Created by: benvenker

• Update copy: should now read:

We currently recommend code monitors on repositories that don’t have a high commit traffic and for non-critical use cases. We are actively working on increasing the performance and fidelity of code monitors to support more sensitive workloads, like a large number of repositories or auditing published code for secrets and other security use cases.

- [ ] Add info box to https://sourcegraph.com/code-monitoring?visible=1 above "All code monitors" section