chore: create issue template

Author: bethesque

.github/ISSUE_TEMPLATE.md

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+# Pre issue-raising checklist
+
+I have already (please mark the applicable with an `x`):
+
+* [ ] Read through the relevant docs at https://docs.pact.io
+* [ ] Upgraded to the latest version of the gem
+* [ ] Checked the CHANGELOG to see if the issue I am about to raise has been fixed
+* [ ] Created an executable example that demonstrates the issue using either a:
+  * Dockerfile
+  * Git repository with a Travis or Appveyor (or similar) build
+
+## Software versions
+
+* **OS**: e.g. Mac OSX 10.11.5
+* **pact mock service:** eg. v 1.23.0
+
+## Expected behaviour
+
+Please complete.
+
+## Actual behaviour
+
+Please complete.
+
+## Steps to reproduce
+
+Provide a repository, gist or reproducible code snippet so that we can test the problem.
+
+## Relevant log files
+
+Please ensure you set logging to `DEBUG` and attach any relevant log files here (or link from a gist).