Modify issue reporting invitation text to improve the quality of reports

Improve issue reporting invitation text to improve the quality of reports (and reduce duplicates or support requests).

Existing text:


Proposed text:

> There's been an error. It might be related to your hosting provider, Git backend provider, Decap configuration, or it might be an actual bug in Decap CMS. Please try to exclude the first three possibilities, ideally by asking for assistance on our Discord support channel. Once you're reasonably sure it's a Decap CMS bug, verify if a similar issue has already been reported: if it has, comment and upvote the issue; if not, open a new issue on GitHub. Opening an issue pre-populates it with the error message and debugging data, but this is just the beginning of writing an issue. You need to explain the issue in detail, explain what you were doing just before the issue occurred, list all possible solutions you tried before opening the issue and include a screenshot.