Fix the "running chaincode as an external service" doc section

The Fabric doc says that "Using this chaincode as an external service model, installing the chaincode on each peer is no longer required"

**But this statement can confuse a user who has an organization with at least 2 endorsing peers:**

**Q:** Do I need to install chaincode on a second endorsing peer too?

**A:** Using an chaincode as an external service model, you will need to install a chaincode package on every peer which will execute it.

_I think that the paragraph should be modified to make it clear that if a user has at least 2 endorsing peers, he must install the chaincode in each peer_

link:
https://hyperledger-fabric.readthedocs.io/en/release-2.4/cc_service.html#running-the-chaincode-as-an-external-service

@denali49, @nikhil550, @ODOWDAIBM, @pamandrejko