Bug: fix typos and grammatical errors in CONTRIBUTING.md

[fasakinhenry]

Describe the bug

There are some typos in the contributing.md file which needs to be fixed

Steps to reproduce

1. Go to contributing.md file and go towards the end to see some of the errors

[kimani400]

“Hi, I’d like to fix the typos and grammatical errors in the CONTRIBUTING.md file. Can I take this up?”