Update README.md [added Hacken and SpearbitDAO for audits]

[johnfawole]

[Please describe your pull request here]

Checklist

• The URL is not already present in the list (check with CTRL/CMD+F in the raw markdown file).
• Each description starts with an uppercase character and ends with a period.
  Example: solc-js - JavaScript bindings for the compiler.
• Drop all A / An prefixes at the start of the description.
• Avoid using the word Solidity in the description.

[bkrem]

Working through the PR backlog that has built up. Thank you for this 🙏