[improve][fn] add docs for supporting reading config options from fil…

…es in Python runner (#544)

docs/functions-runtime-process.md

@@ -22,3 +22,37 @@ functionRuntimeFactoryConfigs:
 ```
 
 For more details, see [code](https://github.com/apache/pulsar/blob/master/pulsar-functions/runtime/src/main/java/org/apache/pulsar/functions/runtime/process/ProcessRuntimeFactoryConfig.java).
+
+### Set runtime parameter with configuration file
+
+Pulsar Functions now supports setting runtime parameters using a configuration file **in Python**. 
+
+**Example**
+
+You can start a Python runtime using the configuration file `config.ini` with the following command.
+
+```shell
+pulsar-admin functions localrun \
+  --py /path/to/python_instance.py \
+  --config-file /path/to/config.ini \
+  --classname MyFunction \
+  --logging_level debug \
+  --inputs persistent://public/default/my-input-topic \
+  --output persistent://public/default/my-output-topic \
+  --log-topic persistent://public/default/functions-logs
+```
+
+` --config-file` is the path to the configuration file. Note that:
+
+- The ` --config-file` should be written in `.ini` format, with each parameter being configured as `key = value`. 
+
+    **Example**
+
+    ```ini
+    [DEFAULT]
+    logging_level = info
+    max_pending_async_requests = 1000
+    max_concurrent_requests = 50
+    ```
+
+- When you set a parameter through both the configuration file and the command line, like `logging_level` in the example above, the value set through the command line will **take precedence over** the one set through the configuration file. As a result, the value of `logging_level` is `debug`.