Docs: Fix incorrect link to Emoji class

[ci skip]

Author: dahlia

docs/concepts/text.md

@@ -138,18 +138,20 @@ The above code will create a text like this:
 
 > Hello, [@fedify@hollo.social](https://hollo.social/@fedify).
 
-### `Emoji` 
+### [`Emoji`]
 
 *This API is available since BotKit 0.2.0.*
 
-If you put an `Emoji` object (provided by Fedify) inside the interpolation,
-it will be rendered as a custom emoji.  You usually get `Emoji` objects from
+If you put an [`Emoji`] object (provided by Fedify) inside the interpolation,
+it will be rendered as a custom emoji.  You usually get [`Emoji`] objects from
 the `Reaction.emoji` property.  For example:
 
 ~~~~ typescript
 text`Here's a custom emoji: ${reaction.emoji}.`
 ~~~~
 
+[`Emoji`]: https://jsr.io/@fedify/fedify/doc/~/Emoji
+
 ### `URL` object
 
 If you put a `URL` object inside the interpolation, it will be rendered as a