Documentation update: external chaincode and index for db
Documentation update: external chaincode and index for db

Signed-off-by: Yury Andreev <f1ac122bfbde1196eb7bad1a29e64739237ec9f6@gmail.com>

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