Added note about precedence (closes #2790)

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@2949 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

railties/environments/development.rb

+# Settings specified here will take precedence over those in config/environment.rb
+
 # In the development environment your application's code is reloaded on
 # every request.  This slows down response time but is perfect for development
 # since you don't have to restart the webserver when you make code changes.

railties/environments/production.rb

+# Settings specified here will take precedence over those in config/environment.rb
+
 # The production environment is meant for finished, "live" apps.
 # Code is not reloaded between requests
 config.cache_classes = true

railties/environments/test.rb

+# Settings specified here will take precedence over those in config/environment.rb
+
 # The test environment is used exclusively to run your application's
 # test suite.  You never need to work with it otherwise.  Remember that
 # your test database is "scratch space" for the test suite and is wiped