docker: update docker instructions to be aware of multi-chain config
docker: update docker instructions to be aware of multi-chain config

This commit contains replacement of previous --rpccert flag on newest
--bitcoin.rpccert flag in docker lnd config.
aakselrod/lnd,LightningNetwork/lnd,ddustin/lnd,LightningNetwork/lnd,AndrewSamokhvalov/lnd,ddustin/lnd,aakselrod/lnd,AndrewSamokhvalov/lnd