docs: add isMalicious threat intelligence platform

[hexablob]

Summary

Add isMalicious to the Other Tools section.

About isMalicious

isMalicious is a threat intelligence platform useful during incident response for:

• Checking IP and domain reputation against multiple threat feeds
• Real-time scoring (0-100 confidence score)
• Threat categorization (phishing, malware, C2, botnet, ransomware)
• Integration with OpenCTI and MISP for automated enrichment

Checklist

• Read the contribution guidelines
• Searched for duplicates
• Only Incident Response tools - ✓ (threat intel lookup for IR)
• Used the correct format
• Placed in alphabetical order