Trivial documentation fix for Signed-off-by

Make consistent the capitalization and punctuation of Signed-of-by examples.

Signed-off-by: Ralph Siemsen <ralphs@netwinder.org>
Acked-by: "Samuel Martin" <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

docs/manual/contribute.txt

@@ -40,7 +40,7 @@ $ git format-patch -M -n -s -o outgoing origin/master
 ---------------------
 
 This will generate patch files in the +outgoing+ subdirectory,
-automatically adding the +signed-off-by+ line.
+automatically adding the +Signed-off-by+ line.
 
 Once patch files are generated, you can review/edit the commit message
 before submitting them using your favorite text editor.
@@ -106,7 +106,7 @@ Some more paragraph giving some more details.
 
 And yet another paragraph giving more details.
 
-Signed-off-by John Doe <john.doe@noname.org>
+Signed-off-by: John Doe <john.doe@noname.org>
 ---
 Changes v2 -> v3:
   - foo bar  (suggested by Jane)

docs/manual/patch-policy.txt

@@ -105,7 +105,7 @@ At the end, the patch should look like:
 ---------------
 configure.ac: add C++ support test
 
-signed-off-by John Doe <john.doe@noname.org>
+Signed-off-by: John Doe <john.doe@noname.org>
 
 --- configure.ac.orig
 +++ configure.ac