Update REPL examples to show usage of query inputs

[tsandall]

The REPL now allows users to specify query inputs by defining a documents under the repl.globals namespace. E.g.,

OPA 0.2.2-dev (commit e83a083, built at 2016-11-25T01:40:36Z)

Run 'help' to see a list of commands.

> package repl.globals
>
> request = {"method": "GET", "path": "/foo"}
>
>
> package abc
> import request
> request
+--------------------------------+
|            request             |
+--------------------------------+
| {"method":"GET","path":"/foo"} |
+--------------------------------+

It would be good to include this in the REPL example so people know the behaviour exists.