Update Pull Request Template

[Kazaf123]

It is hard to understand the pull reuqest when I meet some pull requests that only have code, so I think updating a Pull Request Template will make them more readable. Such as:
######Description

######Check List

######My PR Type is:

Thank you!!

[onlinejudge95]

In the meanwhile, raise the PR. We can discuss about the requirements there.

[mihaimaruseac]

Seems to be spam

[poyea]

It's unclear what you mean by "PR type". As long as one describes his/her PR, say is a code change or a doc change to a specific file, everyone would know and understand. I'd close this as this recommendation is not quite suitable here.