Provide better example configuration in repo

[simonswine]

I think we should provide a better example config file in ./cmd/pyroscope/pyroscope.yaml.

The configuration page in our docs seem to be tricky to understand, as they use a "reference name" for certain sections, which often is confused by users. (example 1, example 2)

All the options should be commented out, ideally generated from the existing structs.

[marcsanmi]

We should check other products when updating the documentation, as they use a similar structure (e.g. Loki's configuration)