DOCS: Add explicit link to PR guidelines in PR template

[seanggani]

• [x] Have you followed the guidelines in our Contributor Guide document?
• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context. List any dependencies that are required for this change:

Add explicit link to PR guidelines in PR template and remove optional comment to ensure standard PR structure

Issue number and link:

New Feature Submissions:

1. [x] Does your submission pass tests?
2. [x] Have you lint your code locally before submission?

Changes to Core Features:

• [ ] Have you added an explanation of what your changes do and why you'd like us to include them?
• [ ] Have you written new tests for your core changes, as applicable?
• [ ] Have you successfully run tests with your changes locally?