Logging undocumented

[Chealer]

Ehcache uses the Simple Logging Facade for Java (SLF4J) for logging. While it may seek simplicity, it remains a facade, i.e. an abstraction which complexifies in a sense, requiring users to choose a provider. Without such a provider, warnings such as "Failed to load class org.slf4j.impl.StaticLoggerBinder" will be logged.

This is well documented in the Logging page of Ehcache 2's documentation, but unfortunately, I can't see any equivalent in version 3's documentation. The page should be at least transferred, but also updated to cover modern providers such as log4j-slf4j2-impl.