[MXNET-1305] Scala interpreter instructions

[zachgk]

Description

Add instructions to the scala_setup page for using the interpreter and link to in the only example featuring the interpreter. It also adds a note that we only support scala 2.11. This should address the problem seen in #13468.

@lanking520 @piyushghai @andrewfayres @aaronmarkham

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [MXNET-$JIRA_ID], where $JIRA_ID refers to the relevant JIRA issue created (except PRs with tiny changes)
• Changes are complete (i.e. I finished coding on this PR)
• Code is well-documented:
• For user-facing API changes, API doc string has been updated.
• For new C++ functions in header files, their functionalities and arguments are documented.
• For new examples, README.md is added to explain the what the example does, the source of the dataset, expected performance on test set and reference to the original paper if applicable
• Check the API doc at http://mxnet-ci-doc.s3-accelerate.dualstack.amazonaws.com/PR-$PR_ID/$BUILD_ID/index.html
• To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

[ankkhedia]

@zachgk Thanks for the contribution!
@mxnet-label-bot add [pr-awaiting-review, Scala]

@lanking520 @piyushghai @andrewfayres
Could you please help review this PR?