Documentation: add 'Getting started' section to documentation

[ikopylov]

This section should contain a step-by-step detailed guide on how to setup single Bob node, multiple Bob nodes and a big Bob cluster. This guide should be easy to reproduce by a beginner.

What it should contains:

1. Where and how to download docker image/RPM package/DEB package/binaries
2. Where to find a sample configuration for node, cluster, logger
3. What to change in configuration files
4. How to start Bob node/nodes/cluster
5. How to verify that it is works properly