Proofread and improve documentation examples

[IgnatBeresnev]

Just adding dokka and generating html works out of the box - no question. However, when trying to configure dokka with more advanced options in a project with kotlin 1.6 and gradle 7.1, the configuration examples would not compile or work for various reasons. Moreover, the CLI documentation is rather ambiguous.

Known issues and action points:

• Make sure provided gradle configuration examples work out of the box for latest major gradle versions
• Make sure example projects have the same configuration as examples in the documentation (documentation seems to be outdated in some places atm)
• Provide a minimal configuration example for groovy scripts (now missing)
• Link to / create an example project for CLI (now missing)
• Provide a minimal example for running dokka cli (we now have only the bare minimum and options are documented separately, but no example as to how to piece it all together in a more complex scenario)
• Proofread option names (a mismatch for CLI packageOptions/perPackageOptions)
• <matchingRegex>kotlin($|\.).*</matchingRegex> mentioned in the docs does not seem to work for a simple maven project, needs to be checked
• usage of samples: How are samples supposed to be used?  #1264