admin(README.md): add @adamtopaz to the maintainers list (#6987)
admin(README.md): add @adamtopaz to the maintainers list (#6987)




Co-authored-by: Scott Morrison <63f04b4d96235eb042cc46d94f14d241d2a26722@gmail.com>
Co-authored-by: Adam Topaz <d27a8cca44e6a02363c9f30139fa030f331183dc@users.noreply.github.com>

leanprover-community/mathlib,leanprover-community/mathlib