[doc] update rst and docstring (#1351)

* update rst

* add zero docstr

* fix docstr

* remove fx.tracer.meta_patch

* fix docstr

* fix docstr

* update fx rst

* fix fx docstr

* remove useless rst

docs/colossalai/colossalai.gemini.rst

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+colossalai.gemini
+=================
+
+.. automodule:: colossalai.gemini
+   :members:
+
+.. toctree::
+   :maxdepth: 2
+
+   colossalai.gemini.memory_tracer
+   colossalai.gemini.ophooks
+   colossalai.gemini.paramhooks
+
+
+.. toctree::
+   :maxdepth: 2
+
+   colossalai.gemini.chunk
+   colossalai.gemini.chunk_mgr
+   colossalai.gemini.gemini_context
+   colossalai.gemini.gemini_mgr
+   colossalai.gemini.placement_policy
+   colossalai.gemini.stateful_tensor
+   colossalai.gemini.stateful_tensor_container
+   colossalai.gemini.stateful_tensor_mgr
+   colossalai.gemini.tensor_placement_policy
+   colossalai.gemini.tensor_utils