README Installation instructions are incorrect and result in 404 response via curl

[jeffreymorrisondev]

The README has vendoring instructions for installing via curl - but it references main instead of master branch so populates the js file with a 404 result instead of the javascript:

curl https://raw.githubusercontent.com/bigskysoftware/ssexi/refs/heads/main/ssexi.js >> ssexi.js

should be

curl https://raw.githubusercontent.com/bigskysoftware/ssexi/refs/heads/master/ssexi.js >> ssexi.js