How to check installer signatures

[overheadhunter]

Fixes #22

Windows

Linux

[overheadhunter]

To add an alternative to a keyserver, here is another trustworthy source for our public key:

curl -sSL https://github.com/cryptobot.gpg | gpg --import -

[SailReal]

@overheadhunter good point, added it in 77a8616