List the 5 logging levels. Attempt to document what each does and some
example use cases.

We have a use case where we want to log internal bmcweb errors. debug is
way too chatty. Want to be able to select the logging level. This is the
documentation for that end goal.

These are loosely followed today and more patches will come to move some
traces to the appropriate level.

In our use case, we don't want to be blown up by a fuzz tester but do
want internal errors. This is the difference between error logging level
and warning logging level. Warning is used for 4xx (e.g. 404) and error
is used for 5xx.

Plan to write a tool to walk the redfish tree and try random Redfish ids
and/or try a open source fuzzing tool. The logging for these 404s should
be warning.

Moved the ## Debug logging section from the README.md to this
DEVELOPING.md. Wanted the logging all together but didn't think we had
enough for a LOGGING.md and README seems too high level for this detail.

Tested: Pushed to my fork and formatting looked good.

Change-Id: I9713a4e674b3f519fec3f3caac0178af8d8d73a8
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>