Document how to disable reactions

[dandv]

The DiscussionEmbed code from the README shows reactions as well as the comment widget. Would be good to document how to disable reactions per widget instance, if that setting exists.

[sumnora]

I figured out how to hide the emojis without using CSS display: none. You can set the settings in *.disqus.com/admin/settings/reactions/ and disable the reactions from there.