README.md: Update access permissions

The default access permission for the README.md file should be 664.

Signed-off-by: George Liu <liuxiwei@ieisystem.com>
Change-Id: Ibf94e02728703b19c71cbb882ce24b87edb88820
diff --git a/README.md b/README.md
old mode 100755
new mode 100644