[FAB-8416] add leader election section
[FAB-8416] add leader election section

In order to answer concerns raised by FAB-8416, this commit adds section
and details explaining leader election operation modes and list
limitations of static config.

Change-Id: I0c0be6cf759c09534eba0160e60a4830ea16360c
Signed-off-by: Artem Barger <6d127d713cb520aa658cf81ac2373d74ffc1958c@il.ibm.com>

jimthematrix/fabric,binhn/fabric,stemlending/fabric,stemlending/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,binhn/fabric,manish-sethi/fabric-sidedb,xixuejia/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,hyperledger/fabric,hyperledger/fabric,manish-sethi/fabric,manish-sethi/fabric-sidedb,xixuejia/fabric,xixuejia/fabric,binhn/fabric,muralisrini/fabric,manish-sethi/fabric,stemlending/fabric,manish-sethi/fabric-sidedb,muralisrini/fabric,jimthematrix/fabric,muralisrini/fabric,stemlending/fabric