add issue template

as in the [plotly.js repo](https://github.com/plotly/plotly.js/issues/new): https://github.com/plotly/plotly.js/blob/master/.github/ISSUE_TEMPLATE.md

Author: cldougl

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,9 @@
+Thanks for your interest in plotly.py!!
+
+Before opening an issue, please search for existing and closed issues. If your problem or idea is not addressed yet, [please open a new issue](https://github.com/plotly/plotly.py/issues/new).
+
+Bug reports **must** be accompanied with a reproducible example. Please use the [latest version](https://github.com/plotly/plotly.py/blob/master/CHANGELOG.md) of plotly.py in your report unless not applicable and specify if you're plotting [online](https://plot.ly/python/getting-started/#initialization-for-online-plotting) or [offline](https://plot.ly/python/getting-started/#initialization-for-offline-plotting).
+
+Note that GitHub issues are reserved for bug reports and feature requests only. Implementation questions should be asked on community.plot.ly (tagged [`python`](https://community.plot.ly/c/api/python)) or on Stack Overflow (tagged [`plotly`](https://stackoverflow.com/questions/tagged/plotly)).
+
+Comments on GitHub issues or pull requests should add content to the discussions. Approbation comments such as *+1* or *I would like this feature to be implemented as well* will be deleted by the maintainers. Please use [GitHub reactions](https://github.com/blog/2119-add-reactions-to-pull-requests-issues-and-comments) instead.