Don’t leave trailing whitespace section

Brings in the no trailing whitespace section from https://github.com/github/objective-c-style-guide/pull/58.
Update README.md
Space out, man.
Merge pull request #7 from github/no-trailing-whitespace

Don’t leave trailing whitespace section
The One True Way
Rationale
Merge pull request #9 from github/coolon

The colon belongs to the identifier
Merge branch 'master' into jspahrsummers-patch-1
Fill in “structs over classes” section