Add debugging docs to test api container locally (#2124)

(cherry picked from commit e92d87a)

Author: deliahu

docs/summary.md

@@ -75,6 +75,7 @@
   * [Python packages](workloads/dependencies/python-packages.md)
   * [System packages](workloads/dependencies/system-packages.md)
   * [Custom images](workloads/dependencies/images.md)
+* [Debugging](workloads/debugging.md)
 
 ## Clients
 

docs/workloads/debugging.md

@@ -0,0 +1,25 @@
+# Debugging
+
+You can test and debug your handler implementation and image by running your API container locally.
+
+The `cortex prepare-debug` command will generate a debugging configuration file named `<api_name>.debug.json` based on your api spec, and it will print out a corresponding `docker run` command that can be used to run the container locally.
+
+For example:
+
+<!-- CORTEX_VERSION_README x2 -->
+
+```bash
+cortex prepare-debug cortex.yaml iris-classifier
+
+> docker run -p 9000:8888 \
+> -e "CORTEX_VERSION=0.34.0" \
+> -e "CORTEX_API_SPEC=/mnt/project/iris-classifier.debug.json" \
+> -v /home/ubuntu/iris-classifier:/mnt/project \
+> quay.io/cortexlabs/python-handler-cpu:0.34.0
+```
+
+Make a request to the api container:
+
+```bash
+curl localhost:9000 -X POST -H "Content-Type: application/json" -d @sample.json
+```