Resolve "Some of the links in the CONTRIBUTING.md file are not working"

Description

Added correct links into the text. Now this links lead to the required destination.

Related Issue

Closes #89 (closed)

How Has This Been Tested?

Clicking on links now lead you to the appropriate file.

Types of changes

• 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:

• 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.