Improve the Load Balancing docs

Tasks

• Improve the Load Balancing docs, including:
  • Confirm and document C Tor behavior on descriptor re-publishing.
  • Basic guide (adapt from this document).
  • Possible architectures (adapt from this document).
  • Combining both approaches.
  • Balancing between servers or just CPUs (since C Tor is single-threaded).

Time estimation

• Complexity: very small (0.5 day)
• Uncertainty: low (x1.1)
• Reference (adapted)