Update FAQ for common errors while code generation (#885)

* update FAQ for common errors

* add specific version information

README.md

@@ -132,6 +132,8 @@ Users can refer to [this document](https://github.com/Azure/azure-rest-api-specs
 
 See [different combination of generation options](https://github.com/Azure/autorest.az/blob/master/doc/how-to-generate-with-different-options.md#most-useful-command-options-combination) for more useful scenarios.
 
+If there is any error while code generation, please check [common errors while code generation](https://github.com/Azure/autorest.az/blob/master/doc/faq.md#common-errors-while-code-generation) for resolutions.
+
 ## Build the Generated Code
 If you want to do a simple try, please go to the az-output-folder that you specified in your readme.az.md, build the wheel file and add the generated file into Azure CLI.
 ```

doc/faq.md

@@ -449,4 +449,26 @@ cli:
             shorthandSyntax: true
 ```
 In this way. we can use `--param-name key1=value1,key2=value2 key1=valuea,key2=valueb` instead of `--param-name key1=value1 key2=value2 key1=valuea key2=valueb` to suggest that we want to input  
-two items (value1, value2) and (valuea, valueb).    
+two items (value1, value2) and (valuea, valueb).
+
+## Common errors while code generation
+The specific version information:
+
+| AutoRest Core  | AutoRest CLI  | Node.js  |
+|:--------------:|:-------------:|:--------:|
+|    3.0.6370    |     3.5.1     |  12.20   |
+
+> ModuleNotFoundError: No module named 'm2r'
+1. Active the Python virtual environment within "@autorest/python" extension;
+2. Execute `pip install m2r`;
+
+> AttributeError: module 'mistune' has no attribute 'BlockGrammar'
+1. Active the Python virtual environment within "@autorest/python" extension;
+2. Execute `pip install mistune==0.8.4`;
+
+> Failed to install or start extension '@autorest/az'
+
+Specify the version of Node.js to **12.20** and the command should be like:
+```
+$ autorest --version=3.0.6370 --az --use=@autorest/az@latest <path-to-the-swagger-readme.md> --azure-cli-extension-folder=<path-to-the-azure-cli-extension-repo>
+```