MARK comments for protocol extensions

Author: gregheo

README.markdown

@@ -232,16 +232,20 @@ class BoardLocation {
 
 When adding protocol conformance to a class, prefer adding a separate class extension for the protocol methods. This keeps the related methods grouped together with the protocol and can simplify instructions to add a protocol to a class with its associated methods.
 
+Also, don't forget the `// MARK` comment to keep things well-organized!
+
 **Preferred:**
 ```swift
 class MyViewcontroller: UIViewController {
   // class stuff here
 }
 
+// MARK: - UITableViewDataSource
 extension MyViewcontroller: UITableViewDataSource {
   // table view data source methods
 }
 
+// MARK: - UITableViewDelegate
 extension MyViewcontroller: UIScrollViewDelegate {
   // scroll view delegate methods
 }