Minor grammar fixes in `contributing.rst`

[krakxn]

Category

Documentation

Description

Minor grammar fixes in contributing.rst.

no doggo T_T

[krakxn]

@charles-cooper Sorry, but is it okay if I follow your suggestion after these? As I did not make a lot of changes, it would be quick to review.

I will bundle it up the next time!

[charles-cooper]

closing as stale on account of unresolved merge conflicts and unresolved review feedback