Chronos: add chronos known issue (#4496)

* add chronos known issue

* modify doc

* modify chronos_known_issue

* modify chronos issue

* modify

* modify issue

* modify chronos_known_issus

docs/readthedocs/source/doc/Chronos/Overview/chronos_known_issue.md

@@ -0,0 +1,62 @@
+# Chronos Known Issue
+## **1. Issue 1**
+**Problem description**
+
+Numpy.ndarray size changed, may indicate binary incompatibility. Expected 88 from C header, got 80 from PyObject. 
+
+**Solution**
+* `pip install -y pycocotools`
+* `pip install pycocotools --no-cache-dir --no-binary :all:`
+* `conda install –c conda-forge pycocotools`
+
+---------------------------
+
+## **2. Issue 2**
+**Problem description**
+
+NotImplementedError: Cannot convert a symbolic Tensor (encoder_lstm_8/strided_slice:0) to a numpy array. 
+
+**Solution**
+
+* `pip install numpy==1.19.5`
+
+---------------------------
+
+## **3. Issue 3**
+
+**Problem description**
+
+StanModel object has no attribute 'fit_class', cause of pip, may be. 
+
+**Solution**
+
+* `pip uninstall pystan prophet –y`
+* `conda install –c conda-forge prophet=1.0.1`
+
+---------------------------
+
+## **4. Issue 4**
+**Problem description**
+
+Exception: No active RayContext. Please call init_orca_context to create a RayContext.
+> ray_ctx = RayContext.get()<br>
+> ray_ctx = RayContext.get(initialize=False)
+
+**Solution**
+
+* Make sure all operations are before `stop_orca_context`. 
+* No other `RayContext` exists before `init_orca_context`. 
+
+---------------------------
+
+## **5. Issue 5**
+**Problem description**
+
+ Sed: error while loading shared libraries: libunwind.so.8: cannot open shared object file: No such file or directory.
+> Only happens when you run `source bigdl-nano-init`. 
+
+**Solution**
+
+* `apt-get install libunwind8-dev` 
+
+---------------------------

docs/readthedocs/source/index.rst

@@ -67,6 +67,7 @@ BigDL Documentation
    doc/Chronos/Overview/chronos.md
    doc/Chronos/Overview/deep_dive.rst
    doc/Chronos/QuickStart/index.md
+   doc/Chronos/Overview/chronos_known_issue.md
 
 .. toctree::
    :maxdepth: 1