Install Git OS X needs to be revised

[vuinguyen]

According to @C4rL: this is a problem:

Under step 2, maybe revise the instruction about installing Xcode. Xcode takes a long time to install. How to deal with this? Also, it's only a problem for older OS's.

Supposedly, the problem is this:
both homebrew and git require Xcode to install on a Mac

One possible revision to the doc:
if they don't already have Xcode installed, continue on to the create a website steps while waiting for Xcode to install

[carlwiedemann]

if they don't already have Xcode installed, continue on to the create a website steps while waiting for Xcode to install

This seems to be the simplest solution here. The main problem we were trying to address is that a student was waiting for about an hour for Xcode to download on the guest wifi at the event.

We realized that students can proceed with the "Create a webpage" or "HTML structure" steps without Xcode, since Xcode isn't necessary until the student needs to use git, which isn't until https://railsbridge.cfapps.io/javascript-installfest/create-a-github-pages-repository

By working on the other steps in parallel, students can make the most of their time at the event.