Add Onionbalance documentation

Tasks

• Decide which section in the Ecosystem can host these docs. Options:
  • New "Base" section, documenting the Onion Services "foundation" software:
    • C Tor.
    • Arti.
    • Onionbalance.
• Add the Onionbalance documentation once it's converted to Onion MkDocs:
  • Setup the repository config.
  • Copy (or include?) relevant MkDocs config.

Time estimation

• Complexity: negligible (0.1 day)
• Uncertainty: low (x1.1)
• Reference (adapted)