[Doc] Expand Multimodal API Reference (#11852)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

docs/source/api/multimodal/parse.md

@@ -0,0 +1,9 @@
+# Data Parsing
+
+## Module Contents
+
+```{eval-rst}
+.. automodule:: vllm.multimodal.parse
+    :members:
+    :member-order: bysource
+```