Add customize apps section to /business

[neynah]

User during testing indicated that many systems allow for companies to do in-house additions and that we should mention somewhere that if a company wants extra features they can build their own apps.

Although it's not a business only feature, I agree that we should make it more clear that it's possible and encouraged to package in-house apps.

[paulproteus]

+1 Could live at https://sandstorm.io/features if that works for the people in your test, but if not, then https://sandstorm.io/business would be good.

[kentonv]

If we put it at /business, we should make sure people don't get confused and think that running your own apps is a business-only feature.