Documentation/notes: document format of notes trees
Separate the specification of the notes format exposed in
git-config.1 from the description of the option; or in other
words, move the explanation for what to expect to find at
refs/notes/commits from git-config.1 to git-notes.1.
Suggested-by: Thomas Rast <trast@student.ethz.ch> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>