Add comparison block to README: orchd vs docker-compose vs systemd vs nomad

[adiled]

The audience needs immediate answers to "how is this different from docker-compose? from raw systemd? from nomad? from pm2?" A short comparison table near the top of the README is high-yield for the effort involved.

Be honest about trade-offs. The audience for service orchestration is technical and skeptical. Oversold copy reads as a red flag.

Action

• Draft a short comparison table or block (4 to 6 lines per alternative is enough).
• Place it near the top of the README, after the pitch and before the install snippet.
• Cover the trade-offs honestly: what orchd does that the alternatives don't, and what the alternatives do that orchd doesn't.

Context
Tracked in the distribution playbook at adiled/distribution.

~ distribution team