Make feature-start setup tracking branch on remote

A single `git push -u` would do the same thing, but asking each user to do that
the very first time they push would be silly. And automatically pushing every
time they create a feature branch would also be silly.

feature.rb

@@ -13,6 +13,10 @@
 
    Git::run_safe("git branch \"#{feature}\" master")
    Git::run_safe("git checkout \"#{feature}\"")
+   # Automatically setup remote tracking branch
+   Git::run_safe("git config branch.#{feature}.remote origin")
+   Git::run_safe("git config branch.#{feature}.merge refs/heads/#{feature}")
+   Git::run_safe("git config branch.#{feature}.rebase true")
 
    puts "Successfully created a new feature-branch: #{feature}"