admin(README.md): add @b-mehta to the maintainers list (#6986)
admin(README.md): add @b-mehta to the maintainers list (#6986)




Co-authored-by: Scott Morrison <63f04b4d96235eb042cc46d94f14d241d2a26722@gmail.com>
Co-authored-by: Bhavik Mehta <9af8340dc2d19f2d10b6cf8ff0f1387bbe986c1a@gmail.com>

leanprover-community/mathlib,leanprover-community/mathlib