Remove trailing whitespace from one line in README
Recommend installing full Xcode in our README (as Boxen now does)

I initially installed Xcode Command Line Tools from the linked
download ( https://developer.apple.com/downloads/index.action ),
rather than by installing the full Xcode. Boxen couldn't find
Xcode, and suggested using 'xcode-select --switch' to set the
path to it. I did that, using only '/' because xcode-select
apparently appends '/usr/bin/' to the path it is given and it
was installed into /usr/bin/. When running Boxen again, brew
tried to run 'xcodebuild --version' which hung with 100% CPU,
as mentioned here:

    https://github.com/mxcl/homebrew/issues/10309#issuecomment-4039128

As later comments there suggest, installing the full Xcode via
the App Store (and then installing Command Line Tools from Xcode's
Downloads tab) puts it instead in /Applications/Xcode.app, and
using this path for xcode-select seemed to solve this issue,
allowing Boxen to do its stuff.

This may be why Boxen recommends installing the full Xcode; that
isn't documented in the commit which added the recommendation to
their README ( c3808d88b6242ce39a17a758473838c375099837 ).

I had to run 'sudo xcode-select --switch /Applications/Xcode.app'
after installing through the full Xcode, but this may have been a
consequence of trying the standalone Command Line Tools first;
this step isn't mentioned in Boxen's README and may be unnecessary
when using full Xcode from the start.
Merge pull request #31 from alphagov/recommend_full_xcode

Recommend installing Command Line Tools via the full Xcode