Add syntastic integration to the readme

Author: keith

README.md

@@ -10,9 +10,28 @@ If you don't have a preferred installation method check out
 ![](https://raw.githubusercontent.com/keith/swift.vim/master/screenshots/screen.png)
 ![](https://raw.githubusercontent.com/keith/swift.vim/master/screenshots/screen2.png)
 
+## [Syntastic](https://github.com/scrooloose/syntastic/) Integration
 
-### Development
+swift.vim can show errors inline from
+[swift package manager](https://github.com/apple/swift-package-manager/)
+or from [swiftlint](https://github.com/realm/SwiftLint) using
+[syntastic](https://github.com/scrooloose/syntastic/).
 
-I plan to continue improving this plugin as I find more issues with
-it. If you find anything strange with highlighting or indention *please*
-[submit an issue](https://github.com/keith/swift.vim/issues/new).
+![](https://raw.githubusercontent.com/keith/swift.vim/master/screenshots/screen3.png)
+
+### Usage
+
+- Install [syntastic](https://github.com/scrooloose/syntastic/)
+
+- swiftpm integration will be automatically enabled if you're running vim
+from a directory containing a `Package.swift` file.
+
+- SwiftLint integration will be automatically enabled if you have
+SwiftLint installed and if you're running vim from a directory
+containing a `.swiftlint.yml` file.
+
+- To enable both at once add this to your vimrc:
+
+```vim
+let g:syntastic_swift_checkers = ['swiftpm', 'swiftlint']
+```