Proofread the existing Proof Market documentation

[NickVolynkin]

The current docs have a few word choice, punctuation, and style issues. Let's fix them before making significant changes like #63.

• [x] First "Guides" section (also rename it to Getting started) #67
  • [x] Move documents to ./getting-started directory, add redirects https://docs.gitbook.com/product-tour/git-sync/content-configuration#how-to-create-a-redirect
• [x] Economics + Supported proof systems #68
• [x] User Guides #71
• [x] Frontend #70
• [x] CMD reference → CLI reference #94
• [x] Terminology #70
• [x] Requester/Producer Flow https://github.com/NilFoundation/proof-market-toolchain/pull/97
• [x] Mina Proof pipeline https://github.com/NilFoundation/proof-market-toolchain/pull/97
• [x] ignore the Misc section

Make branches from the branch https://github.com/nilfoundation/proof-market-toolchain/tree/00-gitbook-docs.

For each chunk of work, open a PR from your branch → 00-gitbook-docs. Make chunks small enough to make 2-3 PRs a day.