docs: adding field descriptions to predefined audio document

Signed-off-by: punndcoder28 <puneethk.2899@gmail.com>

docarray/documents/audio.py

@@ -2,6 +2,8 @@
 
 import numpy as np
 
+from pydantic import Field
+
 from docarray.base_doc import BaseDoc
 from docarray.typing import AnyEmbedding, AudioUrl
 from docarray.typing.bytes.audio_bytes import AudioBytes
@@ -94,11 +96,25 @@ class MultiModalDoc(BaseDoc):
     ```
     """
 
-    url: Optional[AudioUrl]
-    tensor: Optional[AudioTensor]
-    embedding: Optional[AnyEmbedding]
-    bytes_: Optional[AudioBytes]
-    frame_rate: Optional[int]
+    url: Optional[AudioUrl] = Field(
+        description='The url to a (potentially remote) audio file.',
+        example='https://github.com/docarray/docarray/blob/main/tests/toydata/hello.mp3?raw=true',
+    )
+    tensor: Optional[AudioTensor] = Field(
+        description='''Tensor object of the audio which be specified to one of
+        `AudioNdArray`, `AudioTorchTensor`, `AudioTensorFlowTensor`''',
+    )
+    embedding: Optional[AnyEmbedding] = Field(
+        description='Store an embedding: a vector representation of the audio.',
+        example='[[1, 1, 2], [1, 1, 1]]',
+    )
+    bytes_: Optional[AudioBytes] = Field(
+        description='Bytes representation pf the audio',
+    )
+    frame_rate: Optional[int] = Field(
+        description='''An integer representing the frame rate of the audio.''',
+        example=24,
+    )
 
     @classmethod
     def validate(