[x/go.dev] content: add "Creating a badge" section to about page
[x/go.dev] content: add "Creating a badge" section to about page

The about page contains a new section that describes badges
and how to generate them for pkg.go.dev pages

Change-Id: Ibf1139e624efd8b795ac8dd9f4bbb1ab46138867
X-GoDev-Commit: 0129f127d067b330842bd26dcd09cf3ec3225d73

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website