Update the documentation of the raw diff output format

This includes mentioning the initial hash output of diff-tree, and
changes the header to "raw output format" which is more descriptive.
Signed-off-by: NDavid Kågedal <davidk@lysator.liu.se>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/diff-format.txt

-The output format from "git-diff-index", "git-diff-tree",
+Raw output format
+-----------------
+
+The raw output format from "git-diff-index", "git-diff-tree",
 "git-diff-files" and "git diff --raw" are very similar.
 
 These commands all compare two sets of things; what is
@@ -16,6 +19,9 @@ git-diff-tree [-r] <tree-ish-1> <tree-ish-2> [<pattern>...]::
 git-diff-files [<pattern>...]::
         compares the index and the files on the filesystem.
 
+The "git-diff-tree" command begins its ouput by printing the hash of
+what is being compared. After that, all the commands print one output
+line per changed file.
 
 An output line is formatted this way:
 

Documentation/git-diff-files.txt

@@ -43,8 +43,7 @@ omit diff output for unmerged entries and just show "Unmerged".
 -q::
 	Remain silent even on nonexistent files
 
-Output format
--------------
+
 include::diff-format.txt[]
 
 

Documentation/git-diff-index.txt

@@ -34,8 +34,6 @@ include::diff-options.txt[]
 	'git-diff-index' say that all non-checked-out files are up
 	to date.
 
-Output format
--------------
 include::diff-format.txt[]
 
 Operating Modes

Documentation/git-diff-tree.txt

@@ -159,8 +159,7 @@ HEAD commits it finds, which is even more interesting.
 
 in case you care).
 
-Output format
--------------
+
 include::diff-format.txt[]
 
 

Documentation/git-diff.txt

@@ -84,8 +84,7 @@ include::diff-options.txt[]
 	the diff to the named paths (you can give directory
 	names and get diff for all files under them).
 
-Output format
--------------
+
 include::diff-format.txt[]
 
 EXAMPLES