README: symlink from README.md

It looks better as markdown than rendered as text via the markdown tool,
so just symlink it.

Signed-off-by: Sage Weil <sage@redhat.com>

diff --git a/README b/README
new file mode 120000 (symlink)
index 0000000..42061c0
--- /dev/null
+++ b/README
@@ -0,0 +1 @@
+README.md
\ No newline at end of file