Add instructions for custom issue type for JIRA Enterprise

[jasonmacgowan]

fixes #14

Summary

Describe the goal of this PR. Mention any related Issue numbers.

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

The following point can be removed after setting up CI (such as Travis) with coverage reports (such as Codecov)

• I've written tests to cover the new code and functionality included in this PR.

The following point can be removed after setting up a CLA reporting tool such as cla-assistant.io

• I've read, agree to, and signed the Contributor License Agreement (CLA).

[fyunaz]

Hi, thanks for adding this. Are you able to visit the following URL to sign the CLA? https://cla-assistant.io/slackhq/goSDL?pullRequest=15

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}