Merge branch 'jc/diff-format-doc' into maint

The documentation incorrectly said that C(opy) and R(ename) are the
only ones that can be followed by the score number in the output in
the --raw format.

* jc/diff-format-doc:
  diff-format doc: a score can follow M for rewrite

Documentation/diff-format.txt

@@ -66,7 +66,8 @@ be committed)
 
 Status letters C and R are always followed by a score (denoting the
 percentage of similarity between the source and target of the move or
-copy), and are the only ones to be so.
+copy).  Status letter M may be followed by a score (denoting the
+percentage of dissimilarity) for file rewrites.
 
 <sha1> is shown as all 0's if a file is new on the filesystem
 and it is out of sync with the index.