Added williamchrisp username

[williamchrisp]

Description

Exercise (e.g. C01-E01): Updating Student name

Student Name: William Chrisp

Updated the team-external-students with my github username

Type of change

• [ ] Exercise Submission (one exercise per PR)
  • [ ] This PR is just for one exercise of a class
  • [ ] PR name follows the pattern <github-username>/<exercise-number>
  • [ ] Added exercise files inside folder /classes/<class- number>/exercises/<exercise-number>/<github-username>/
    • [ ] Review exercise submission steps
• [ ] Class content (instructors/admins)
• [ ] Documentation update
• [X] Repo management