updated readme for debugging

README.md

@@ -98,6 +98,51 @@ To pull an image from an upstream pipeline or stage, the following information i
    - Specify the artifact id of the external artifact that belongs to the upstream job
 
    ![](images/fetch_artifact_task.png)
+
+## Troubleshooting
+
+### Enable Debug Logs
+
+#### If you are on GoCD version 19.6 and above:
+
+Edit the file `wrapper-properties.conf` on your GoCD server and add the following options. The location of the `wrapper-properties.conf` can be found in the [installation documentation](https://docs.gocd.org/current/installation/installing_go_server.html) of the GoCD server.
+
+```properties
+# We recommend that you begin with the index `100` and increment the index for each system property
+wrapper.java.additional.100=-Dplugin.cd.go.artifact.docker.registry.log.level=debug
+```
+
+If you're running with GoCD server 19.6 and above on docker using one of the supported GoCD server images, set the environment variable `GOCD_SERVER_JVM_OPTIONS`:
+
+```shell
+docker run -e "GOCD_SERVER_JVM_OPTIONS=-Dplugin.cd.go.artifact.docker.registry.log.level=debug" ...
+```
+
+#### If you are on GoCD version 19.5 and lower:
+
+* On Linux:
+
+    Enabling debug level logging can help you troubleshoot an issue with this plugin. To enable debug level logs, edit the file `/etc/default/go-server` (for Linux) to add:
+
+    ```shell
+    export GO_SERVER_SYSTEM_PROPERTIES="$GO_SERVER_SYSTEM_PROPERTIES -Dplugin.cd.go.artifact.docker.registry.log.level=debug"
+    ```
+
+    If you're running the server via `./server.sh` script:
+
+    ```shell
+    $ GO_SERVER_SYSTEM_PROPERTIES="-Dplugin.cd.go.artifact.docker.registry.log.level=debug" ./server.sh
+    ```
+
+* On windows:
+
+    Edit the file `config/wrapper-properties.conf` inside the GoCD Server installation directory (typically `C:\Program Files\Go Server`):
+
+    ```
+    # config/wrapper-properties.conf
+    # since the last "wrapper.java.additional" index is 15, we use the next available index.
+    wrapper.java.additional.16=-Dplugin.cd.go.artifact.docker.registry.log.level=debug
+    ```
 
 ## License