Add ValueError to PartialEmoji.read docstring

discord/partial_emoji.py

@@ -233,6 +233,26 @@ class PartialEmoji(_EmojiTag, AssetMixin):
         return f'{Asset.BASE}/emojis/{self.id}.{fmt}'
 
     async def read(self) -> bytes:
+        """|coro|
+
+        Retrieves the content of this asset as a :class:`bytes` object.
+
+        Raises
+        ------
+        DiscordException
+            There was no internal connection state.
+        HTTPException
+            Downloading the asset failed.
+        NotFound
+            The asset was deleted.
+        ValueError
+            The PartialEmoji is not a custom emoji.
+
+        Returns
+        -------
+        :class:`bytes`
+            The content of the asset.
+        """
         if self.is_unicode_emoji():
             raise ValueError('PartialEmoji is not a custom emoji')