moved vlsi flow control description

docs/VLSI/Hammer.rst

@@ -25,6 +25,17 @@ Hooks
 
 Hooks are modifications to steps or actions that are programmatically defined in a Hammer configuration.
 
+
+VLSI Flow Control
+-----------------
+Sometimes we want more fine-grained control of the VLSI flow than at the action level.
+The Hammer flow supports being able to start/stop before/after any of the steps in a particular action. 
+See the `Hammer documentation on Flow Control <https://docs.hammer-eda.org/en/latest/Hammer-Use/Flow-Control.html>`__ for a full list and description of the options.
+The ``Makefile`` in the ``vlsi`` directory passes this extra information via the ``HAMMER_EXTRA_ARGS`` variable.
+This variable can also be used to specify additional YAML configurations that may have 
+changed or been omitted from the inital build.
+
+
 Configuration (Hammer IR)
 =========================