Add SJS Unit Test Example to Landing Page

[jamesagardner]

I think these are good to call out, but I'm thinking it'd be nice to show something ASAP on this page.

For example, after briefly describing marklogic-unit-test, hop into an example. Show a bare minimum library module (in SJS), like an "echo" function. Then show what the test module looks like. Then show a screenshot of running the test module via the UI. Then show a screenshot of running the test via Intellij (will require that skeleton Java class, may not be worth mentioning that yet).

That covers the main use case - testing library functions. A secondary use case is using marklogic-junit to test endpoints. I wouldn't go into detail about that on the home page though - instead, provide a link to a Wiki page (or the README for marklogic-junit).

I think the screenshots of the UI and the Intellij (or Eclipse) test runner will carry the most value, because it immediately shows the user how they'll be running the tests.

Originally posted by @rjrudin in #73

[prestonmcgowan]

I copied sample-tests.xqy and created sample-tests.sjs

const test = require("/test/test-helper.xqy");

test.assertTrue(true);
test.log("sample-tests COMPLETE....");

[rjrudin]

I think the new docs do a much better job helping the user understand how to get going.