feat/getting started improvements

[timkoopmans]

Improvements to the getting started documentation:

• Incorporate feedback from Felipe
• Reference Operator and Alternator where appropriate
• Improve examples in query design / data types
• remove advanced / hanging topics (tombstones etc)
• minor typos, correct links and formatting

[annastuchlik]

@timkoopmans Could you squash the commits before I merge this PR?