doc: add GitHub issue and pull-request templates !cosmetic

Author: acdha

.github/issue_template.md

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+* [ ] Tested with the latest Haystack release
+* [ ] Tested with the current Haystack master branch
+
+## Expected behaviour
+
+## Actual behaviour
+
+## Steps to reproduce the behaviour
+
+1.
+
+## Configuration
+
+* Operating system version:
+* Search engine version:
+* Python version:
+* Django version:
+* Haystack version:

.github/pull_request_template.md

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+# Hey, thanks for contributing to Haystack. Please review [the contributor guidelines](http://django-haystack.readthedocs.org/en/latest/contributing.html) and confirm that [the tests pass](http://django-haystack.readthedocs.org/en/latest/running_tests.html) with at least one search engine.
+
+# Once your pull request has been submitted, the full test suite will be executed on https://travis-ci.org/django-haystack/django-haystack/pull_requests. Pull requests with passing tests are far more likely to be reviewed and merged.