Document emoji picker (#4338)

Co-authored-by: Tom Moor <tom.moor@gmail.com>

shared/editor/rules/emoji.ts

@@ -1,6 +1,6 @@
-import nameToEmoji from "gemoji/name-to-emoji.json";
 import MarkdownIt from "markdown-it";
 import emojiPlugin from "markdown-it-emoji";
+import { nameToEmoji } from "../lib/emoji";
 
 export default function emoji(md: MarkdownIt) {
   // Ideally this would be an empty object, but due to a bug in markdown-it-emoji