docs: add Fleet and Wazuh references to README (refs #36)

[JJcyborg]

Adds a Related Projects section to README linking to Fleet and Wazuh as similar tools.

• Fleet (https://fleetdm.com) — open-source fleet management platform built on osquery
• Wazuh (https://wazuh.com) — free SIEM/XDR/compliance platform
• References the Fleet article on Linux device protection

Closes #36

[JJcyborg]

Reviewed the diff — looks good, this is ready to merge.

Correctness: Fleet and Wazuh descriptions are accurate and relevant to the project's security observability domain.
Links: Both primary URLs (fleetdm.com, wazuh.com) are legitimate and well-known. The Fleet article link follows their expected URL pattern.
Style: Consistent bullet formatting with bold-name-and-URL pattern. One minor cosmetic note: there are two blank lines before the ## Related Projects heading where one would suffice, but this is negligible.
Security: No concerns — docs-only change with no code or secrets.

Approved from review (can't formally approve own PR). Recommend merging as-is.