Add a note on memory usage and perfomance impact in "Securing your Web services with Spring-WS" chapter of reference documentation [SWS-45]

**[Steven Devijver](https://jira.spring.io/secure/ViewProfile.jspa?name=devijvers)** opened **[SWS-45](https://jira.spring.io/browse/SWS-45?redirect=false)** and commented


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**Affects:** 1.0 M1
