Update README for docker hub
Update README for docker hub

We asked a new person to follow the guide to start the docker using the image from docker hub yesterday, and it seems the word "replace" makes it confusing if the user is not cloning the EOSIO/eos github repo and just want to start the docker container immediately.
EOSIO/eos,EOSIO/eos,EOSIO/eos,EOSIO/eos,EOSIO/eos