docs: update links to contributing guide

[ChristianMurphy]

Checklist

• [x] the individual contributor license agreement is signed
• [x] commit message follows commit guidelines
• [x] tests are included
• [x] documentation is changed or added
• [x] new security keys and comments added to security.properties
• [x] new general keys and comments added to portal.properties
• [x] any changes that impact configuration or the database DDL added to CHANGES.md
• x[] have been updated with new phrases
• [x] view conforms with WCAG 2.0 AA

Description of change

This corrects the link to the contributing guide, which is now in the .github folder

[ChristianMurphy]

Do you see a reason it should stay in the .github folder?

At the time root and .github were the two magic folders. It looks like there are currently 3 magic folders https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions/creating-a-default-community-health-file

GitHub will use and display default files for any repository owned by the account that does not have its own file of that type in any of the following places: The root of the repository The .github folder The docs folder

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Also, not specifically needed, but the Jasig content path segment could be switched to uPortal-Project.

Good point, I'll update this