Convert the command line interface docs to docusaurus

[dckesler]

• The relevant docs are inside of docs/command-line-interface/.
• The urls should match our current docs starting at https://docs.celo.org/command-line-interface/introduction.
• We should decide what a matching document would be title for the current category in gitbook at https://docs.celo.org/command-line-interface/commands.

[dckesler]

We'll need to come up with a solution to automate this differently now that docs is moving out into its own repository.