Added `source` and valuable flags to Podfile template

All Podfiles should specify a `source` and with the growing number of Swift applications, having the `use_frameworks!` flag available is also very helpful.

Also, including the `inhibit_all_warnings!` will usually save a google search, as well. Most people haven't memorized all of the common cocoapod flags.

lib/cocoapods/command/init.rb

@@ -56,8 +56,13 @@ module Pod
         podfile = ''
         podfile << "xcodeproj '#{@project_path}'\n\n" if @project_path
         podfile << <<-PLATFORM.strip_heredoc
+          source 'https://github.com/CocoaPods/Specs.git'
           # Uncomment this line to define a global platform for your project
           # platform :ios, '6.0'
+          # Uncomment this line if you're using Swift
+          # use_frameworks!
+          # Uncomment this line to ignore all warnings from all pods
+          # inhibit_all_warnings!
         PLATFORM
 
         project.targets.each do |target|