add a CONTRIBUTING.md file

add a CONTRIBUTING.md file, copied verbatim from the "Pull Requests" section in README.md
Ignore Vim untitled and unsaved buffer swapfiles

Vim creates buffer swapfiles starting at .swp for buffers that are
active but untitled and unsaved.
Unignore "packages/*/build" in VisualStudio.gitignore.
Merge pull request #694 from anurse/patch-1

Unignore "packages/*/build" in VisualStudio.gitignore.
Adding CocoaPods to gitignore
Merge remote-tracking branch 'matzew/master' (pull request #418)
Remove Podfile.lock from Objective-C ignores

Per discussion in #148.
Merge pull request #493 from strugee/master

This repository didn't have a CONTRIBUTING.md file. Now it does.
Merge pull request #576 from nysa/master

Ignore Vim untitled and unsaved buffer swapfiles
ignore kernel object files
added secret_token.rb

I added secret_token.rb file to the gitignore as there are public repos sharing it.
Merge pull request #714 from mattjeffery/ignore_kernel_objects

Ignore kernel object files
Merge pull request #735 from aldo-roman/patch-1

added secret_token.rb
add .xccheckout to Objective-C gitignore

This is a file that Xcode 5 uses for version control, doesn't need to be checked in. Also see http://stackoverflow.com/a/18448100/1877078
Merge pull request #774 from bdewater/patch-1

add .xccheckout to Objective-C gitignore
ensure single trailing newline
Merge pull request #801 from github/fix-trailing-newlines

Ensure single trailing newline