Update Dockerfile (#229)

updating to include command for new self-hosted quickstart guide

Author: Adi Atzmony

Diff for: jfrog-quickstart-examples/Dockerfile

@@ -1,2 +1,5 @@
+#Option 1: for cloud subscription
 FROM ${SERVER_NAME}.jfrog.io/${VIRTUAL_REPO_NAME}/ubuntu:16.04
+#Option 2: for Self-Hosted subscription. Remove the above cloud command and use the below command
+#FROM ${Artifactory_URL:Artifactory_PORT}/${VIRTUAL_REPO_NAME}/ubuntu:16.04
 CMD printf "CONGRATULATIONS!!! You have just set up your first Docker repository with the new JFrog Platform!"