Update README desc and add table of contents
Update README desc and add table of contents

I plan on adding more to this document in the future so adding a
table of contents.  Also clarified the description to not imply
everything is based on the journal.

Signed-off-by: Matt Spinler <c000c989d08c98662d98f15448f11de169feb92d@us.ibm.com>
Change-Id: Idc846ae0afb2dae76bb176ff1f0d879a72270c50

openbmc/phosphor-logging,openbmc/phosphor-logging,openbmc/phosphor-logging,openbmc/phosphor-logging