Add Troubleshooting section about antivirus false positive

[philrz]

As discussed in a thread on public Slack, a user recently made us aware that our suricata-update.exe binary gets flagged as possible malware. Here's my attempt at writing an article to address the topic proactively or via link should it come up again with other users. In addition to pointing our own users at it, I expect I might also be able to reference it from:

1. The "comments" area of the Community tab for the VirusTotal entry, as was recommended to me by one community user in that Slack thread.
2. Forms or emails with which we might contact the antivirus providers to make the case that it be considered a false positive.

I admit this content was a little awkward to write. Obviously I'd prefer to not have gone into such extensive detail when describing the origin of the file i question. At the same time, just saying "don't worry, it's a false positive" would have felt sleazy (isn't that exactly what a malware-provider would say?), and saying "it's open source... go convince yourself" without some detail would have felt like a lazy attempt to distract. Given that we're open source, I figured I might as well put it all out there in the open.

In addition to our own PR review process, I'll also bring this PR to the attention of the community user that offered some initial guidance and will hold off on merging until they've had a chance to offer feedback as well.

[philrz]

I got a passing grade from the community. 😉

[philrz]

I've also added a comment at VirusTotal pointing back at the article. When I have some cycles I'll look into what's involved with contacting the anti-virus providers to see if there's a chance of this being marked as benign at the source such that this becomes a non-issue.