[#74316] document JSON WP workflows

Add README examples for the new machine-readable Work Package
flows: inspect with children, parent-aware create dry-runs, and
schema-driven update dry-runs.

https://community.openproject.org/projects/cli/work_packages/74316

Author: myabc

README.md

@@ -150,6 +150,10 @@ op create workpackge --project 11 'Document new CLI tool'
 
 # Same command with shorthands and directly open it in a browser to continue working on it.
 op create workpackge -p11 'Document new CLI tool' -o
+
+# Validating the creation of a child work package without persisting it.
+# The parent determines the project automatically.
+op create workpackage --parent 74316 --type Implementation 'Build reusable skill' --dry-run --json
 ```
 
 #### Listing