Adding documentation about beans.xml. Closes #815.

The text you quoted is really about Java EE, but the previous not. The previous paragraph describe Containers in a generic way:

```
When determining which archives are bean archives, the container must consider:
    Library jars, EJB jars or application client jars
    The WEB-INF/classes directory of a war
    Directories in the JVM classpath
```

I'm confused because the spec is too weak/poor. So I agree with you that we need to keep your docs too clear as possible. I'll update the text ASAP. Thanks to discuss this point to clarify our opinions.