"For Contributors" document is out-of-date

[mark-dce]

STORY
As a new hydra dev, I would like to run the test suite, so that I can contribute via PRs.

DETAILS
When I read the Modifying and Testing the hydra-head Gem section of the README, it links me to the Instructions for Contributors page on the wiki. The instruction there reference hydra-jetty, etc.

When I try to run rake ci after following those instructions, I get a stack dump:

$ rake ci
rake aborted!
LoadError: cannot load such file -- solr_wrapper
/Users/mark/Documents/workspace/_no_backup/RubymineProjects/hydra-head/Rakefile:6:in `<top (required)>'
(See full trace by running task with --trace)

ACCEPTANCE
EITHER

• delete the wiki page and update the reference in the README to just point at CONTRIBUTING.md. In which case, I don't really get information on how to run the tests.
  OR
• update the wiki page to reflect current practice so I can follow the instructions successfully.

[mark-dce]

I've made updates to the "for the impatient" section. The following sections still need to be re-written to explain how to test using engine cart in more detail - i.e. how to setup to run individual tests.

[jcoyne]

Super!