`README.md` div mistake

[PhilJbt]

<div param="value"></div> cannot be written as <div param="value" />, this doesn't close the div and messes up the rest of the HTML.

https://github.com/mattmezza/bulmahead/blob/3799ae5b418e5e944752ee643f7c13547305241a/README.md?plain=1#L13