added diff keyword to changelog/docs

CHANGELOG.md

@@ -123,6 +123,7 @@ Ansible Changes By Release
   of handling IP addresses. (PR# 26566)
 * datetime filter updated to use default format of datetime.datetime (ISO8601)
 * The junit plugin now has an option to report a junit test failure on changes for idempotent testing.
+* New 'diff' keyword allows setting diff mode on playbook objects, overriding command line option and config.
 
 #### New Callbacks:
 - full_skip

docs/docsite/keyword_desc.yml

@@ -18,6 +18,7 @@ connection: Allows you to change the connection plugin used for tasks to execute
 delay: Number of seconds to delay between retries, this setting only makes sense when used with 'until'.
 delegate_facts: Boolean that allows you to apply facts to delegated host instead of inventory_hostname.
 delegate_to: Host to execute task instead of the target (inventory_hostname), connection vars from the delegated host will also be used for the task.
+diff: Toggle to make tasks return 'diff' information or not.
 environment: A dictionary that gets converted into environment vars to be provided for the task upon execution.
 fact_path: Set the fact path option for the fact gathering plugin controlled by ``gather_facts``.
 failed_when: Conditional expression that overrides the task's normal 'failed' status.