README: use markdown syntax

This allows repository browsers like GitHub to display the content of
the file nicely formatted.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

README → README.md

-////////////////////////////////////////////////////////////////
-
-	Git - the stupid content tracker
-
-////////////////////////////////////////////////////////////////
+Git - the stupid content tracker
+================================
 "git" can mean anything, depending on your mood.

t/t7001-mv.sh

@@ -102,7 +102,7 @@ test_expect_success \
 test_expect_success \
     'adding another file' \
-    'cp "$TEST_DIRECTORY"/../README path0/README &&
+    'cp "$TEST_DIRECTORY"/../README.md path0/README &&
      git add path0/README &&
      git commit -m add2 -a'