Adding example for multiple fields command (#1148)

Co-authored-by: Roshan-sy <roshan-sy@github.com>

azure-devops/azext_devops/dev/boards/work_item.py

@@ -43,6 +43,7 @@ def create_work_item(work_item_type, title, description=None, assigned_to=None,
     :param discussion: Comment to add to a discussion in a work item.
     :type discussion: str
     :param fields: Space separated "field=value" pairs for custom fields you would like to set.
+    In case of multiple fields : "field1=value1" "field2=value2".
     Refer https://aka.ms/azure-devops-cli-field-api for more details on fields.
     :type fields: [str]
     :param open: Open the work item in the default web browser.