[slf4j-user] FAQ suggestion: "How do I configure log levels for SLF4J?"

[Joachim Durchholz]

Motivation: I used to confuse SLF4J and Logback myself, so that makes at 
least two persons who had that problem.
I believe that it could be a pretty common problem because SLF4J and 
Logback come from the same source and have a very similar documentation 
style. Plus you deal with the SLF4J API on a daily basis and kinda 
forget that it's really the logging backend that does the real work and 
needs to be configured.

Suggestion: Add the following section to the FAQ:

Q: How do I configure what logging levels are shown?
A: Not on SLF4J. SLF4J provides the API that your code uses for logging, 
but the real action happens in the backend: Logback, Log4j, etc., and 
it's there that you configure the logging levels.