Linked DOCUMENTATION.md in PULL_REQUEST_TEMPLATE.md

[IamLRBA]

Description

Please explain the changes you made here.

Related Issue

Please link to the issue this PR resolves: [issue #]

Motivation and Context

Why is this change required? What problem does it solve?

How Has This Been Tested?

Please describe in detail how you tested your changes.

Screenshots (if appropriate):

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

Go over all the following points, and put an x in all the boxes that apply.

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.