Document 'git-blame --incremental'

Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-blame.txt

@@ -8,7 +8,7 @@ git-blame - Show what revision and author last modified each line of a file
 SYNOPSIS
 --------
 [verse]
-'git-blame' [-c] [-l] [-t] [-f] [-n] [-p] [-L n,m] [-S <revs-file>]
+'git-blame' [-c] [-l] [-t] [-f] [-n] [-p] [--incremental] [-L n,m] [-S <revs-file>]
             [-M] [-C] [-C] [--since=<date>] [<rev>] [--] <file>
 
 DESCRIPTION
@@ -63,6 +63,10 @@ OPTIONS
 -p, --porcelain::
 	Show in a format designed for machine consumption.
 
+--incremental::
+	Show the result incrementally in a format designed for
+	machine consumption.
+
 -M::
 	Detect moving lines in the file as well.  When a commit
 	moves a block of lines in a file (e.g. the original file
@@ -158,6 +162,47 @@ parents, using `commit{caret}!` notation:
 	git blame -C -C -f $commit^! -- foo
 
 
+INCREMENTAL OUTPUT
+------------------
+
+When called with `--incremental` option, the command outputs the
+result as it is built.  The output generally will talk about
+lines touched by more recent commits first (i.e. the lines will
+be annotated out of order) and is meant to be used by
+interactive viewers.
+
+The output format is similar to the Porcelain format, but it
+does not contain the actual lines from the file that is being
+annotated.
+
+. Each blame entry always starts with a line of:
+
+	<40-byte hex sha1> <sourceline> <resultline> <num_lines>
++
+Line numbers count from 1.
+
+. The first time that commit shows up in the stream, it has various
+  other information about it printed out with a one-word tag at the
+  beginning of each line about that "extended commit info" (author,
+  email, committer, dates, summary etc).
+
+. Unlike Porcelain format, the filename information is always
+  given and terminates the entry:
+
+	"filename" <whitespace-quoted-filename-goes-here>
++
+and thus it's really quite easy to parse for some line- and word-oriented
+parser (which should be quite natural for most scripting languages).
++
+[NOTE]
+For people who do parsing: to make it more robust, just ignore any
+lines in between the first and last one ("<sha1>" and "filename" lines)
+where you don't recognize the tag-words (or care about that particular
+one) at the beginning of the "extended information" lines. That way, if
+there is ever added information (like the commit encoding or extended
+commit commentary), a blame viewer won't ever care.
+
+
 SEE ALSO
 --------
 gitlink:git-annotate[1]