Change External wiki, for Rails 4.1 don't allow mass assignment

[aj07mm]

There are mass assignment examples on the code but this is not allowed for Rails 4.1, there should be an specification or a sample for both with mass assignment and without.

[joshbuker]

@aj07mm if you want to take a stab at updating the wiki page, we would appreciate the help. The wiki is free and open for anyone to edit.