Issue template imporved

[neeraj3029]

Fixes #489

Checklist

• [x] I have read the Contribution & Best practices Guide and my PR follows them.
• [x] My branch is up-to-date with the Upstream master branch.
• [ ] The unit tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)
• [ ] All the functions created/modified in this PR contain relevant docstrings.

Short description of what this resolves:

Issue template now asks for screenshots. Also, the line Please let us know if you can work on it or the issue should be assigned to someone else only conveys message to user, so was commented.

[neeraj3029]

@ms10398 Done the required changes.