Evaluation-focussed getting started guide did not include instructions regarding the need for and installation of the JDK

# User role

Evaluating user
# Trying to achieve

Attempting to follow the getting started guide that offers to help with evaluation so I can gain intuitions about what JanusGraph can do, how to interact with it usefully, and the costs of managing its infrastructure all of which I'm attempting to do in order to avoid excluding it as a useful tooling choice.
# Steps to reproduce

Follow the guide at http://docs.janusgraph.org/latest/server.html#server-getting-started

# Expected outcome

Output as listed in the guide
# Actual outcome

```
$ bin/janusgraph.sh start
jps command not found. Put the JDK's jps binary on the command path.
```
# Other info
```
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 17.10
Release: 17.10
Codename: artful
```

Start with the server getting started guide at http://docs.janusgraph.org/latest/server.html#server-getting-started and review the evaluation steps around bin/janusgraph.sh start. Document the JDK requirement and installation or PATH prerequisite for jps, then verify that the guide's listed output can be reached on the reported Ubuntu setup.

Written by the indexing model from the issue text.