Finalize mdbook for Holiday Milestone (12/31)

[ra0x3]

• Change the "Receipts" section to "What can I index" and better explain what types/data users can index
• Add explanations for Tx data -- copy it from the fuel-tx docs here https://github.com/FuelLabs/fuel-specs/tree/master/src/protocol/tx_format
• Add specific setup details according to platform (we sort've have this but it makes some assumptions. no assumptions should be made)
  • This is a PITA but no avoiding it
• Add details on how to get setup with a database (postgres & sqlite)
  • This should be added to the Quickstart too
• All example usage should use the plugin where possible
• Add a section to "Components" that explains how to get started with the Fuel node