Update README to point Enterprise Users to website instead
Update README to point Enterprise Users to website instead

Since Enterprise users are still a minority, now they get a nicely
formatted help article instead of their own paragraph taking up space in
our README file.

IQAndreas/github-issues-import,lukesmith/github-issues-import,simonfork/github-issues-import,jonboulle/github-issues-import,danmichaelo/github-issues-import,LalatenduMohanty/github-issues-import,abrkn/github-issues-import,crawford/github-issues-import,nrc/github-issues-import