Fix markup and minor grammar improvements in Code_of_conduct.md (GH-13640)

The old link had a > in the url which prevented the browser from jumping down to the correct section on that page.

That PSF page itself has an error: There's a duplicate "the" in that paragraph that needs to be removed: "...and conform to **the the** Python Community Code of Conduct."

While I was editing this file, I also fixed some grammar and bolded the 3 important keywords so that they catch the viewer's eyes. I can revert these changes if they are unwanted.

Thanks.