[doc] fix composenotaligned (#1774)

doc/fluid/api/io/ComposeNotAligned.rst

@@ -11,3 +11,4 @@ ComposeNotAligned
     :inherited-members:
     :noindex:
 
+This indicates an error state of compose API, which will raise when outputs of readers are not aligned.

doc/fluid/api_cn/io_cn/ComposeNotAligned_cn.rst

+..  THIS FILE IS GENERATED BY `gen_doc.{py|sh}`
+    !DO NOT EDIT THIS FILE MANUALLY!
+
+.. _api_fluid_io_ComposeNotAligned:
+
+ComposeNotAligned
+-----------------
+
+..  autoclass:: paddle.fluid.io.ComposeNotAligned
+    :members:
+    :inherited-members:
+    :noindex:
+
+表示一种错误状态，说明调用compose API时, reader的输出数据没有对齐。

scripts/api_white_list.txt

@@ -6,3 +6,4 @@ transpiler_cn/memory_optimize_cn.rst
 transpiler_cn/release_memory_cn.rst
 transpiler_cn/RoundRobin_cn.rst
 optimizer_cn/Dpsgd_cn.rst
+io_cn/ComposeNotAligned_cn.rst