README: add blurb on async testing

Fixes #132.
Codesign for iOS

Fix for issue #79 matches Nimble settings from
https://github.com/Quick/Nimble/commit/517aea52ca54a142af5a9edc12ff80a9f
0a5277f
Fix submodule clone command

Remove extra 'add'
Consistent folder name capitalization

vendor -> Vendor
Update submodules after adding them

Otherwise you have two empty folders in Vendor/
Merge pull request #137 from joemasilotti/submodules

Update submodules section of README
Merge pull request #136 from jbosse/master

Codesign for iOS