You can find that in docker-compose files folder chaincode (fabric-samples/chaincode) is mounted to /opt/gopath/src/github.com/chaincode and in the script.sh variable CC_SRC_PATH is set to github.com/chaincode/chaincode_example02/go/, so if you want to use your own chaincode in the first-network solution you should put it to folder chaincode and set up CC_SRC_PATH this varibles is used in utils.sh file
peer chaincode install -n mycc -v ${VERSION} -l ${LANGUAGE} -p ${CC_SRC_PATH} >&log.txt