Leftover reference to master branch in CONTRIBUTING.md after conflict resolution in PR #443

[leftkats]

Describe the bug
There is a leftover line in the CONTRIBUTING.md file referring to the old master branch. This seems to be the result of an incorrect or incomplete conflict resolution during the merge of Pull Request #443.

To Reproduce
Steps to identify the issue:

Go to CONTRIBUTING.md

Check line 31

Notice the outdated reference to master instead of main

Expected behavior
All branch references should point to main to reflect the current default branch of the repository.

Additional context
I've already created a feature branch to resolve this issue. Please review and let me know if you'd prefer a separate pull request for it.

Please check #440

Thanks @DhanushNehru