handler: add descriptions for each method
handler: add descriptions for each method

Describe each method's goals and how they vary by the current state.

Change-Id: Idbdd0b39a92abec6920b591660c1cd9f4fa4315b
Signed-off-by: Patrick Venture <36c53fa43f47f3fd67cb2fc38031827244d18a1f@google.com>

openbmc/phosphor-ipmi-flash