Add screenshot of sample report to the README

[spier]

Closes #150.

As the visual changes matters here, make sure the review the rendered version of the proposed change too.

Proposed Changes

• Add screenshot of sample report to the README.
• Add section title for the "Metrics" information
• Move sentence about the origins of this project to the intro (the bit about the GitHub OSPO)

Things to consider/review

• is the screenshot too large? I am mostly concerned about the height of the image.
• do we like the place in the README where the screenshot appears? could also be moved below the workflow sample if we prefer. As a user I personally like to see first "what will I get when using this" before I learn "how do I use this".
• so reduce height of the screenshot, we could cut off anything below "this report was generated with". we could also cheat and remove some of the issues from the full list of issues :)

Readiness Checklist

Author/Contributor

• If documentation is needed for this change, has that been included in this pull request
• run make lint and fix any issues that you have introduced
• run make test and ensure you have test coverage for the lines you are introducing

Reviewer

• Label as either bug, documentation, enhancement, infrastructure, or breaking

[spier]

@Okabe-Junya please take a look.

[Okabe-Junya]

I think it's wonderful!! Thank you for adding such clear screenshots!!

[zkoppert]

Improvements look great! Thanks @spier for putting up this pull request and @Okabe-Junya for reviewing!