Added GitHub diff markdown syntax

[thevedicdeveloper]

Diff markdown syntax is a special syntax worked only on the GitHub markdown fileds.

[thevedicdeveloper]

Hi @atapas, I am adding a special syntax which is limited to GitHub markdown fields only. I would appreciate it if you please have a look at the changes.

Please do let me know if you want to move the syntax to any particular order.

Happy HacktoberFest

[thevedicdeveloper]

@atapas, Can you please label this pull request as hacktoberfest. As this is my First Pull Request in my life 😄

[atapas]

@thevedicdev Resolve the merge conflct.

Also, the link is broken...I think because of the / character

[thevedicdeveloper]

Thanks for assigning me @atapas.

I have resolved the conflict, please have a look.

[thevedicdeveloper]

Hi @atapas, please review the pull request.