Overview

The contributing guidelines for mycroft-core need minor updates to correct a broken links, provide a bit more clarity for new contributors, and ensure consistency between the use of 'issue' and 'issues'.

Proposed Resolution

• Fix broken links, so creating an issue links to the actual mycroft-core issues / testing pages, not 404 or redirects
• Add code block showing how to add an upstream remote after forking
• Update recommendations to use singular 'issue' in all locations, rather than a mix of 'issue' and 'issues'
• Various copy changes for clarity

I am happy to take care of these items and will be submitting a PR shortly that reflects the changes. I think this will provide increased clarity moving forward to those who wish to contribute.

Additionally, I think we could improve the clarity of the pre-PR rebase codeblock, but this is more personal preference--I know everyone has their own individual style on how they reset / rebase from upstream and merge changes.