Review spec intro

[schomatis]

• Rework overview diagram. The TODO is self explanatory.

• Provide a simpler version of the deals on chain diagram.

• Add introductory texts to the major systems listed, such as

  • https://filecoin-project.github.io/specs/#systems__filecoin_nodes
  • https://filecoin-project.github.io/specs/#systems__filecoin_files
  • VM might not be necessary as its explained in the first section.

• Annotated comments in place in this branch: master...schomatis/review/intro

[yiannisbot]

This is now ongoing with this PR: #1168 - reviews welcome. Closing this issue.