Readme: Best practices

[kazhuravlev]

Readiness probes look pretty simple in usual dialogs, but sometimes they are complicated in real-life applications. We need to understand which dependencies should be monitored and which ones are truly important. We also have other questions, such as "Should we make ping requests to other services in our system that we are using?"

In practice, we need to carefully consider our decisions about these and other questions. To help our users make the right choices, we should describe best practices in our README file.