Changed comment section to be more explicit. I had an issue with roll…

…ing back a migration and couldn't understand why 'rake db:reset' didn't work.

guides/source/migrations.md

@@ -684,8 +684,9 @@ version to migrate to.
 The `rake db:reset` task will drop the database, recreate it and load the
 current schema into it.
 
-NOTE: This is not the same as running all the migrations - see the section on
-[schema.rb](#schema-dumping-and-you).
+NOTE: This is not the same as running all the migrations. It will only use the contents 
+of the current schema.rb file. If a migration can't be rolled back, 'rake db:reset'
+may not help you. To find out more about dumping the schema see [schema.rb](#schema-dumping-and-you).
 
 ### Running Specific Migrations