[documentation] Log field now required on all edits

[Addison Berry]

Just to keep everyone up to date, thanks to oadaeh and dww, the log  
field is now required on all handbook page edits.

http://drupal.org/node/308675

Try to keep 'em short and useful. If you are doing lots of minor  
tweaking to a page, feel free to use "Minor edits" or "Minor tweaks"  
but if you make real changes please say what they were. This is  
especially important if you move a page since diff won't show anything.

- Addi (add1sun)