Enhance scam warning

[FWDekker]

I also received a scam email, as described in #98. In #99, a warning was added to the README. This PR enhances that warning in two ways.

1. Explicitly makes the part #98 link to There is spam happening involving usage of this project/script #98, because this does not happen automatically in READMEs, and some people may not know that #98 is supposed to link to an issue.
2. Use GitHub-flavoured Markdown alert to make the warning more visible.

I also fixed what I think was a typo in the first sentence.

[CLAassistant]

All committers have signed the CLA.

[akim-bow]

Thanks!