(chore) update slack link, add discord link
(chore) update slack link, add discord link

isagalaev/highlight.js,carlokok/highlight.js,highlightjs/highlight.js,carlokok/highlight.js,highlightjs/highlight.js,carlokok/highlight.js,carlokok/highlight.js,highlightjs/highlight.js,isagalaev/highlight.js,highlightjs/highlight.js