README: vxworks: Fix typo overwride

%s/overwride/override/

Signed-off-by: Naoki Hayama <naoki.hayama@lineo.co.jp>
diff --git a/README b/README
index 377e6aa..1be60ed 100644
--- a/README
+++ b/README
@@ -618,7 +618,7 @@
 		serverip, gatewayip, hostname, othbootargs.
 		It loads the vxWorks image pointed bootfile.
 
-		Note: If a "bootargs" environment is defined, it will overwride
+		Note: If a "bootargs" environment is defined, it will override
 		the defaults discussed just above.
 
 - Cache Configuration: