Documentation: clarify that there is no lifecycle support

Hi,
after using Guice for a few weeks, to my surprise today I discovered that Guice has no support for fundamental lifecycle callbacks like @PostConstruct, and there is no intention to add it https://github.com/google/guice/issues/62#issuecomment-115452493

As @PostConstruct is a critical feature when you do field/set injection (no constructor injection), I am now in the situation to be forced to switch to another DI framework (likely Spring or CDI Weld), as Guice's workarounds are far too verbose or error prone (eg, InjectionListener or constructor injection).

It would be great if the documentation of Guice could be updated to clearly state that @PostConstructor is and will not be supported, eg a section called "No Lifecycle Support" under https://github.com/google/guice/wiki/Bindings