Add contributing guidelines

[RupamGanguly46]

Write CONTRIBUTING.md to help Hacktoberfest contributors know how to contribute.

[RISHABH4SAHNI]

Hi @RupamGanguly46 , can i work on this issue for hactoberfest.
Please assign thiss task to me.

[RupamGanguly46]

Hi @RupamGanguly46 , can i work on this issue for hactoberfest. Please assign thiss task to me.

Alright, please do it within 2 days : )

[RISHABH4SAHNI]

@RupamGanguly46
I’ve created the PR with the requested changes. Could you please review it at your convenience? If everything looks good, we can go ahead with the merge. Since I’m participating in Hacktoberfest, a quick review and action would be really appreciated.
#55