Fixed doc markup that was causing RDoc to ignore part of the README

README.rdoc

@@ -152,7 +152,7 @@ are called before and after the processing of each attachment), and the
 attachment-specific "before_<attachment>_post_process" and
 attachment-specific "before_<attachment>_post_process" and
 "after_<attachment>_post_process". The callbacks are intended to be as close to
 "after_<attachment>_post_process". The callbacks are intended to be as close to
 normal ActiveRecord callbacks as possible, so if you return false (specifically
 normal ActiveRecord callbacks as possible, so if you return false (specifically
--- returning nil is not the same) in a before_ filter, the post processing step
+- returning nil is not the same) in a before_ filter, the post processing step
 will halt. Returning false in an after_ filter will not halt anything, but you
 will halt. Returning false in an after_ filter will not halt anything, but you
 can access the model and the attachment if necessary.
 can access the model and the attachment if necessary.