Create a pull request template for github

We're starting to see PRs appear without any JIRA, explanation etc. These are going to be ignored without them.

It's possible to [create a PR text template](https://help.github.com/articles/creating-a-pull-request-template-for-your-repository/) under .github/PULL_REQUEST_TEMPLATE

We can do such a template, which provides template summary points, such as:

• which JIRA
• if against an object store, how did you test it?
• if its a shell script, how did you test it?