Xcode Command Line Tools do not require developer account anymore

[sebroeder]

The information in https://github.com/middleman/middleman-guides/blame/master/source/basics/install.html.markdown#L15-L17 is outdated. (At least) since OS X 10.9 one can install the Command Line Tools without a Apple Developer account directly from the command line with:

xcode-select --install

This will display the following dialog:

Should we propose this mechanism as the default installation method for both Xcode and Command Line Tools? If yes, should we provide additional information for older systems?

[tdreyno]

Does xcode-select exist without installing Xcode?

[sebroeder]

Does xcode-select exist without installing Xcode?

Yes. Starting with OS X 10.9 (I think, have to validate this in a VM) Apple installed some shims in /usr/bin that trigger dialogs like the one above to install Xcode/Command Line Tools, Java, etc. on demand. In the background it uses Apple Software Update to install this stuff. This works on every OS X 10.9.x and 10.10.x system out of the box.

[tdreyno]

Great! Lets update the docs.