These patches improve help output in a few cases where I found it lacking.

3 patches for repository http://darcs.net/screened:

patch 704efbf89326b8195c9919e73b15176cc0668db7
Author: Ben Franksen <ben.franksen@online.de>
Date:   Sat Sep 29 13:23:00 CEST 2018
  * update help for defaults file(s)
  
  The information given there was partly out-dated.

patch 4db7dedb12416d907bfbb72452524b243ead6165
Author: Ben Franksen <ben.franksen@online.de>
Date:   Sun Sep 30 19:27:51 CEST 2018
  * add subcommand 'darcs help preferences'
  
  This is exactly the same as the chapter in the manual, slightly re-formatted
  for terminal output.

patch 7c1f5b8288f3baa5472ce20e6bb74dfbacea179a
Author: Ben Franksen <ben.franksen@online.de>
Date:   Mon Oct  1 10:46:04 CEST 2018
  * improve help for _darcs/prefs/sources

Attachments

• patch-preview.txt
• unnamed
• update-help-for-defaults-file_s_.dpatch

>   * update help for defaults file(s)

Fine

>  * add subcommand 'darcs help preferences'

Fine

>  * improve help for _darcs/prefs/sources

Fine (I haven't cross-checked what you wrote against the code, but 
it sounds right to me).