Documentation/log: add a CONFIGURATION section

Add a configuration section summarizing variables that affect the
log family of commands.

Cc: Thomas Rast <trast@student.ethz.ch>
Cc: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-log.txt

@@ -132,6 +132,48 @@ Discussion
 
 include::i18n.txt[]
 
+Configuration
+-------------
+
+See linkgit:git-config[1] for core variables and linkgit:git-diff[1]
+for settings related to diff generation.
+
+format.pretty::
+	Default for the `--format` option.  (See "PRETTY FORMATS" above.)
+	Defaults to "medium".
+
+i18n.logOutputEncoding::
+	Encoding to use when displaying logs.  (See "Discussion", above.)
+	Defaults to the value of `i18n.commitEncoding` if set, UTF-8
+	otherwise.
+
+log.date::
+	Default format for human-readable dates.  (Compare the
+	`--date` option.)  Defaults to "default", which means to write
+	dates like `Sat May 8 19:35:34 2010 -0500`.
+
+log.showroot::
+	If `false`, 'git log' and related commands will not treat the
+	initial commit as a big creation event.  Any root commits in
+	`git log -p` output would be shown without a diff attached.
+	The default is `true`.
+
+mailmap.file::
+	See linkgit:git-shortlog[1].
+
+notes.displayRef::
+	Which refs, in addition to the default set by `core.notesRef`
+	or 'GIT_NOTES_REF', to read notes from when showing commit
+	messages with the 'log' family of commands.  See
+	linkgit:git-notes[1].
++
+May be an unabbreviated ref name or a glob and may be specified
+multiple times.  A warning will be issued for refs that do not exist,
+but a glob that does not match any refs is silently ignored.
++
+This setting can be disabled by the `--no-standard-notes` option,
+overridden by the 'GIT_NOTES_DISPLAY_REF' environment variable,
+and supplemented by the `--show-notes` option.
 
 Author
 ------