Add documentation for find_or_create_by_{attribute}! method.

activerecord/lib/active_record/base.rb

@@ -208,6 +208,9 @@ module ActiveRecord #:nodoc:
   #   # Now 'Bob' exist and is an 'admin'
   #   User.find_or_create_by_name('Bob', :age => 40) { |u| u.admin = true }
   #
+  # Adding an exclamation point (!) on to the end of <tt>find_or_create_by_</tt> will
+  # raise an <tt>ActiveRecord::RecordInvalid</tt> error if the new record is invalid.
+  #
   # Use the <tt>find_or_initialize_by_</tt> finder if you want to return a new record without
   # saving it first. Protected attributes won't be set unless they are given in a block.
   #

railties/guides/source/active_record_querying.textile

@@ -1109,6 +1109,8 @@ Client.where(:first_name => 'Andy').first_or_create!(:locked => false)
 # => ActiveRecord::RecordInvalid: Validation failed: Orders count can't be blank
 </ruby>
 
+As with +first_or_create+ there is a +find_or_create_by!+ method but the +first_or_create!+ method is preferred for clarity.
+
 h4. +first_or_initialize+
 
 The +first_or_initialize+ method will work just like +first_or_create+ but it will not call +create+ but +new+. This means that a new model instance will be created in memory but won't be saved to the database. Continuing with the +first_or_create+ example, we now want the client named 'Nick':