Clarify where to run sbt package from in Exercise 5

[willfurnass]

If you run it from the wrong place then unfortunately sbt still builds something and doesn't present a sensible error:

[will@mybox ~]$ mkdir someemptydir
[will@v ~]$ cd someemptydir
[will@mybox someemptydir]$ sbt package
[info] Set current project to someemptydir (in build file:/home/will/someemptydir/)
[info] Updating {file:/home/will/someemptydir/}someemptydir...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[info] Packaging /home/will/someemptydir/target/scala-2.10/someemptydir_2.10-0.1-SNAPSHOT.jar ...
[info] Done packaging.
[success] Total time: 1 s, completed 15-Feb-2017 13:08:36
[will@mybox someemptydir]$ 

This causes confusion in Exercise 5 as students run sbt package in the wrong place which then appears to do something sensible but find that the file they then want to pass to spark-submit hasn't been created. However, they have a .jar with a different name that doesn't do anything useful.

Could be addressed by

• Emphasising the need to run sbt package in the same dir as the build 'recipe' (project.sbt)
• Stress the significance of the present working directory: how to check it, change it and that that it can differ from the present working directory in MobaXTerm's file browser. (Issue Clarify distinction between MobaXTerm terminal and file browser present working directories #5)