We've had some difficulty coming up with a good name for the file
that gets included in all of the exercise READMEs for a given track.

These are global hints, like how to run the test suite, which are
relevant to all the exercises on a track.

We started with SETUP.md in the root of the repository, then renamed
that to exercises/TRACK_HINTS.md because SETUP.md was misleading and
confusing, but then we realized that TRACK_HINTS.md was a bit ambiguous
and confusing as well.

Finally we settled on putting the file in the docs directory, since
this is user-facing documentation, and calling the file
EXERCISE_README_INSERT.md

See https://github.com/exercism/meta/issues/5 for context.

Per https://github.com/exercism/docs/blob/81399dc1c87e384be9fada77f599df38f795691d/contributing-to-language-tracks/exercise-readmes.md#exercise-readmes

The contents of this file will be included in each of the README.md
files that are delivered along with the test suites in the exercism
problems.

It's probably useful to provide a generic description of how to run
the tests, as well as a link to the language-specific help page or
useful documentation.

This will cause the correct directory structure to be created when fetching.

Gradle can be run directly on Mac/Linux/Windows and
auto-download dependencies (much like sbt for Scala),
as well as simplify IDE integration.

Add appropriate .gitignore for this sub-tree.

For developers, to add a new exercism:

    cp -r _template new-exercism
    # create test in new-exercism/src/test/java/SampleTest.java
    git add new-exercism

Users will be able to just run "./gradlew check" to run tests.

To use this template to create a new assignment,
simply cp _template to the name of your new assignment
and drop in the appropriate tests.