Mention requirement of 'wheel' package for Universal Wheels

[fboender]

Building "Universal Wheels" requires the "wheel" package to be installed. The manual doesn't mention this. This pull request fixes that.

[theacodes]

@fboender thanks for this, I'd prefer if you moved the install the wheel library part up into the preceding section title Wheels because it's equally application if you're building universal or platform wheels.

[fboender]

Will do!

…

On Thursday, 6 April 2017, Jon Wayne Parrott ***@***.***> wrote: @fboender <https://github.com/fboender> thanks for this, I'd prefer if you moved the install the wheel library part up into the preceding section title Wheels because it's equally application if you're building universal or platform wheel.s — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#273 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ACXNy-siW0gd-6Vj0LPdJebFQ2TJ18ccks5rtV0QgaJpZM4LNZVl> .

[theacodes]

Closing in favor of #299