Fix minor doc typos

[ratmice]

Checklist

• CI Checked:
  • [ ] cargo fmt has been ran
  • [ ] cargo clippy reports no issues
  • [ ] cargo test succeeds
  • [ ] cargo rend3-doc has no warnings
  • [ ] cargo deny check issues have been fixed or added to deny.toml
• Manually Checked:
  • [ ] relevant examples/test cases run
  • [ ] changes added to changelog
    • [ ] Add credit to yourself for each change: Added new functionality @githubname.

Related Issues

Description