Added solution to N-Queen Problem in java

[pavleen14]

Description

Provided a comprehensive approach to N-Queen Problem in java using Backtracking.

Reference Issue number #444

Type of change

Choosing one or more options from the following as per the nature of your Pull request. NOTE: Check boxes using [x]

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [x] Documentation Update

Checklist:

• [x] I have named my files and folder, according to this project's guidelines.
• [x] My code follows the style guidelines of this project.
• [x] My Pull Request has a descriptive title. (not a vague title like Update index.md)
• [x] I have commented on my code, particularly in hard-to-understand areas.
• [x] I have created a helpful and easy to understand README.md, with problem description and my name.
• [x] I have included a requirements.txt file (if external libraries are required.)
• [x] My changes do not produce any warnings.
• [x] I have starred this repository.
• [x] I have added a working sample/screenshot of the script.
• [x] I have checked for trailing spaces in file names and none have them.