doc bug for git-patch-id ?

I just discovered that 
  
  git log -p $ref | git patch-id 

works in place of a corresponding loop using git show | git patch-id

This makes a script I'm hacking on about 10 times faster. 

Am I correct in thinking this should be documented better in the man
page?  At least the intent of the source "generate_id_list" seems to be
to support multiple patches on stdin.

I can probably work up a doc patch; of course if somebody else actually
knows what the doc should say is welcome to write it ;).

David