docs and bug fixed

docs/component/online.rst

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+.. _online:
+
+=================================
+Online Serving
+=================================
+.. currentmodule:: qlib
+
+
+Introduction
+=============
+In addition to backtesting, one way to test a model is effective is to make predictions in real market conditions or even do real trading based on those predictions.
+``Online Serving`` is a set of module for online models using latest data,
+which including `Online Manager <#Online Manager>`_, `Online Strategy <#Online Strategy>`_, `Online Tool <#Online Tool>`_, `Updater <#Updater>`_. 
+
+`Here <https://github.com/microsoft/qlib/tree/main/examples/online_srv>`_ are several examples for reference, which demonstrate different features of ``Online Serving``.
+If you have many models or `task` need to be managed, please consider `Task Management <../advanced/task_management.html>`_.
+The `examples <https://github.com/microsoft/qlib/tree/main/examples/online_srv>`_ maybe based on `Task Management <../advanced/task_management.html>`_ such as ``TrainerRM`` or ``Collector``.
+
+Online Manager
+=============
+
+.. automodule:: qlib.workflow.online.manager
+    :members:
+
+Online Strategy
+=============
+
+.. automodule:: qlib.workflow.online.strategy
+    :members:
+
+Online Tool
+=============
+
+.. automodule:: qlib.workflow.online.utils
+    :members:
+
+Updater
+=============
+
+.. automodule:: qlib.workflow.online.update
+    :members: