Small fixes to make it easier to try out the demo

[localhostdotdev]

"add requirements"

Was not obvious that wireshark or even wireshark 3.0.0 (latest) is required, doesn't work on old versions (kind of mentioned already in the README but not really).

"join path instead of using / for potential windows compatibility"

At the very least, it keeps it a bit consistent with the rest of the file.

"handle tsark command execution errors"

Instead of a generic "JSON parsing failed" error, print stderr from the tshark command.

"fix default paths for demo arguments and working default paths for other demo arguments"

Also not obvious that the default paths are to non-existent files. And some paths had a probably old name in them.

I would understand that the defaults for handshake.pcap, header.json would be the ones in the current directory as it seems that's the way the program is probably used and tested so this change is just an hint at having a better behavior for those options, maybe having a clearer error would help.

"ignore vendor/ directory"

It's probably in every go dev .gitgnore_global file, but I'm not a go dev and didn't have so it polluted quite a bit my working directory.

Anyway, thanks.

(This PR is not meant to be merged, maybe closer to a list of current issues I found while trying the demo)

(The trailing of white spaces is just a bonus offered by my .vimrc :) )

[gabbifish]

Thank you so much for this PR! All these are really helpful fixes (and thanks for catching the reference_fingerprintsa typo, d'oh). Merging.

[localhostdotdev]

Oh, thanks for merging this! I'm still trying it out and will try to make PR and/or issues when I have issues.

[gabbifish]

Yup, I was happy to merge because these were all very clear and concise changes :) Please submit issues/PRs as you see fit!