DOC: Clean up instructions in ISSUE_TEMPLATE
* Minor grammar fixes + clarification on where to paste the output of `pd.show_versions()` to ensure that it renders properly.
* Additional notes about ways to filter out duplicates and / or resolve issues by upgrading.
Not sure why Circle CI makes it less convenient to skip builds:

https://circleci.com/docs/1.0/skip-a-build/ thanks!