Reflect the reality that some W3C standards are voluntary and some not

Fixes w3c#177

Author: darobin

Vision/Vision.bs

@@ -106,7 +106,7 @@ Markup Shorthands: markdown yes
 	where diverse voices from around the world
 	and from different organizations and industries
 	work together to evolve the web by building consensus
-	on voluntary global standards for Web technologies.
+	on global standards, some voluntary and some not, for Web technologies.
 
 	W3C embeds its core values and principles in the Web's architecture.
 	To build a better future, W3C must rise even further