added: contribution guidelines file

[suhasasumukh]

To ensure a safe, respectful, and inclusive environment for all contributors and users. This code will serve as a guideline for behavior, promoting diversity, reducing conflicts, and attracting a wider range of perspectives.

fixes: https://github.com/OpenBMB/ChatDev/issues/238

[cryptictech]

Actually, this appears to be a duplicate of #239

[suhasasumukh]

Actually, this appears to be a duplicate of #239

I will add more contributing guidelines

[suhasasumukh]

@cryptictech please look at the latest push - I have outlined the guidelines better