Updated link to "past pull requests" to point to unoplatform/calculator

[marknoble]

Initial link was to Microsoft/calculator pull requests. They could also provide valuable insight on the code review process, but reviewing closed PRs for the unoplatform/calculator project could be even more informative.

GitHub Issue (If applicable): #

PR Type

What kind of change does this PR introduce?

• Documentation content changes

What is the current behavior?

Current behavior links people to another project to learn about the experience in this project.

What is the new behavior?

I just updated the link to point to this project instead of the parent for an even better example of the experience in checking into this project.

How changes were validated:

• Manually compared the two links.
• New link is more appropriate to current project.
• No visible change other than being routed to closed PRs from unoplatform/calculator instead of microsoft/calculator.

Other information

Internal Issue (If applicable):