Update docs on cylc set (#804)

It now sets success pathway outputs even if optional

Author: MetRonnie

src/user-guide/interventions/index.rst

@@ -166,8 +166,8 @@ Set Task Outputs
          :width: 75%
 
       By default, this sets all :term:`required outputs <required output>` for
-      the task, which usually includes ``succeeded``.
-      To specify the output(s) you would like to set,
+      the task, including ``submitted``, ``started`` and ``succeeded`` (even
+      if those are optional). To specify the output(s) you would like to set,
       press the pencil icon next to the "Set" command .
 
    .. tab-item:: Tui
@@ -177,8 +177,8 @@ Set Task Outputs
          :width: 75%
 
       By default, this sets all :term:`required outputs <required output>` for
-      the task, which usually includes ``succeeded``.
-      To specify the output(s) you would like to set,
+      the task, including ``submitted``, ``started`` and ``succeeded`` (even
+      if those are optional). To specify the output(s) you would like to set,
       use ``cylc set --output``.
 
    .. tab-item:: CLI
@@ -189,8 +189,8 @@ Set Task Outputs
          $ cylc set <workflow>//<task>
 
       By default, this sets all :term:`required outputs <required output>` for
-      the task, which usually includes ``succeeded``.
-      To specify the output(s) you would like to set,
+      the task, including ``submitted``, ``started`` and ``succeeded`` (even
+      if those are optional). To specify the output(s) you would like to set,
       use the ``--output`` option.
 
 You can also :ref:`set task prerequisites <interventions.set-task-prerequisites>`.