Add user testimonials

[edwardchalstrey1]

Requested enahancement or feature

After #13

• Deepmind testimonial - Ian Gemp:

  Gambit is my first stop for exploring a cornucopia of classical techniques for solving games. Its breadth of solvers is unparalleled.

• Research professor
  • Possibly Bernhard von Stengel. Maybe better someone else further from the project
• Someone who uses for teaching

[edwardchalstrey1]

@tturocy One thing we forgot to discuss today, do you have suggestions for person 2 & 3 above?

[tturocy]

This will probably be something that will arise naturally as we start cataloguing better papers that meaningfully cite Gambit. For teaching @rahulsavani has a few courses which we intend will be testing some Gambit-using teaching materials and will be a source for that.