finish WDL and wait for supervisor's checking

Author: Zhang-Zhenning

modelzoo/features/EmbeddingVariable/WDL/SavedModel_Serving.md

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+## How to use prepare_savedmodel.py to get savedmodel
+
+- Current support model: \
+BST, DBMTL, DeepFM, DIEN, DIN, DLRM, DSSM, ESMM, MMoE, SimpleMultiTask, WDL
+
+- Usage: \
+ For every model listed above, there is a prepare_savedmodel.py. To run this script please firstly ensure you have gotten the checkpoint file from training. To use prepare_savedmodel.py, please use:
+
+  ```
+    cd [modelfolder] 
+    python prepare_savedmodel.py --checkpoint [ckpt path]
+  ``` 
+ - If you choose --bf16 during training stage, please also add it above. For example:
+
+   ```
+    cd [modelfolder] 
+    python prepare_savedmodel.py --bf16 --checkpoint [ckpt path]
+   ``` 
+
+
+ - Example: \
+  This is an example for BST model without bf16 feature
+   ```
+    cd modelzoo/BST
+    python prepare_savedmodel.py  --checkpoint ./result/model_BST_1657777492
+   ``` 
+
+ - Output: \
+  The savedmodel will be stored under ./savedmodels folder
+
+
+## How to use start_serving.cc to retrieving serving result
+
+- Functionality: \
+start_serving.cc provides functionality such that you can get serving result after getting the savedmodel.
+
+- Parameter: 
+  1. At the start of main(), there is a file_path variable. Please substitude it to your own evaluation file path (the format should be the same as training one)
+  2. Please edit the savedmodel and checkpoint path in the model_config which is at the very begining.
+
+- Usage: 
+  1. Please edit BUILD file to add the start_serving
+  2. Please make sure you have installed serving part properly
+  3. Then go back to the Deeprec folder and do as the follows, assuming the cc_binary name in BUILD is "wdl_demo":
+   ``` 
+   bazel build //serving/processor/tests:wdl_demo
+   bazel-bin/serving/processor/tests/wdl_demo
+   ``` 
+  
+
+
+