livy/.github/PULL_REQUEST_TEMPLATE

## What changes were proposed in this pull request?

(Please fill in changes proposed in this fix)
Iinclude a link to the associated JIRA and make sure to add a link to this pr on the JIRA as well)

## How was this patch tested?

(Please explain how this patch was tested. E.g. unit tests, integration tests, manual tests)
(If this patch involves UI changes, please attach a screenshot; otherwise, remove this)

Please review https://livy.incubator.apache.org/community/ before opening a pull request.