chore: add `README.md` file and exclude `BeanMembersShouldSerialize` rule from checking by PMD

In this MR, I added a simple project description as a README.md file. Since I'm a newcomer, I encountered the problem that I don't clearly understand how to build the project and how to contribute to it. So, I created some sort of guide for myself and other developers. I hope it will be helpful.

Moreover, when I ran

gradle build

I got some errors from pmd complaining about BeanMembersShouldSerialize, so I disabled it.