Docs: resubmit a Process from a ProcessNode (#5579)

Add documentation on how to resubmit a previously completed process.

Co-authored-by: Sebastiaan Huber <mail@sphuber.net>

docs/source/howto/run_codes.rst

@@ -400,6 +400,20 @@ After :ref:`setting up your computer <how-to:run-codes:computer>` and :ref:`sett
 
 After this, use ``verdi process list`` to monitor the status of the calculations.
 
+.. tip::
+
+    If you ever need to resubmit a previous calculation with modified inputs,
+    you can get a pre-populated copy of its process builder with
+
+    .. code-block:: python
+
+        builder = load_node(<IDENTIFIER>).get_builder_restart()
+        # If needed, the builder can now be modified as usual before being run or submitted
+        submit(builder)
+
+    where ``<IDENTIFIER>`` is the ``PK`` or ``UUID`` (or label) of your *calculation*.
+
+
 See :ref:`topics:processes:usage:launching` and :ref:`topics:processes:usage:monitoring` for more details.