Update README for Cursor config setup

[sakshisaxena]

Summary

Updates the Cursor section in the README to use the current .cursor/rules/*.mdc project rule format instead of the deprecated .cursorrules file.

Changes

• Replace .cursorrules instructions with .cursor/rules/sonatype-mcp.mdc
• Include rule frontmatter (description, alwaysApply) per current Cursor conventions
• Note global rules via Cursor Settings → Rules as an alternative

Test plan

• Markdown renders correctly
• Instructions match current Cursor project rules layout