Add README opening description and Related projects section

[seoulpro]

Summary

• Add an opening paragraph below the H1: "Embertop reads CPU, memory, load average, and web-server access logs on a single host and draws them as one continuously updating terminal view, so request traffic and system pressure are visible side by side without running a metrics stack."
• Keep the italic tagline directly beneath it.
• Add a ## Related projects section with two links:
  • process-leash — limits for individual process trees, where Embertop reports the host totals they contribute to.
  • tallyburn — a companion terminal monitor for token usage instead of host resources.

The README previously opened on the tagline alone. No behavior or configuration changes.

Testing

Not run (documentation-only change).