ACTION-487 Review and polish Overview section

I've tweaked it a bit. Comments and suggestions welcome: 


This specification deals with the trust decisions that users must make 
online, and with ways that user agents support them in making safe and 
informed decisions where possible.
In order to achieve that goal, this specification includes recommendations 
on the presentation of identity information and other security context 
information by Web user agents. We also include recommendations on 
handling errors in security protocols. The error handling recommendations 
both minimize the trust decisions left to users, and  represent known best 
practice in inducing users toward safe behavior where they have to make 
these decisions. To complement the interaction and decision related parts 
of this specification, 7 Robustness addresses the question of how the 
communication of context information needed to make decisions can be made 
more robust against attacks.
This document specifies user interactions with a goal toward making 
security usable, based on known best practice in this area. Subsequent 
testing of this specification will include conformance, interoperability, 
and usability teting. 
This specification comes with two companion documents: [WSC-USECASES] 
documents the use cases and assumptions that underly this specification. 
[WSC-THREATS] documents the Working Group's threat analysis.