Modify init script in Gitpod. Don't build, just print a usage line.

Author: jingedawang

.gitpod.yml

@@ -3,6 +3,6 @@
 # and commit this file to your remote git repository to share the goodness with others.
 
 tasks:
-  - init: ./gradlew build
+  - init: echo -e "You can test any algorithms here. Try run BFPRT with following command:\n./gradlew run -PclassName='select.BFPRT'"