update documentation for the multi-port support in physical pb_pin

docs/source/manual/arch_lang/annotate_vpr_arch.rst

@@ -136,8 +136,12 @@ The ``circuit_model_name`` should match the given name of a ``circuit_model`` de
 
   - ``physical_mode_pin="<string>" creates the link of ``port`` of ``pb_type`` between operating and physical modes. This syntax is mandatory for every primitive ``pb_type`` in an operating mode ``pb_type``. It should be a valid ``port`` name of leaf ``pb_type`` in physical mode and the port size should also match. 
 
+    .. note:: Users can define multiple ports. For example: ``physical_mode_pin="a[0:1] b[2:2]"``. When multiple ports are used, the ``physical_mode_pin_rotate_offset`` should also be adapt. For example: ``physical_mode_pin_rotate_offset="1 0"``)
+
   - ``physical_mode_pin_rotate_offset="<int>"`` aims to align the pin indices for ``port`` of ``pb_type`` between operating and physical modes, especially when an operating mode contains multiple ``pb_type`` (``num_pb``>1) that are linked to the same physical ``pb_type``. When ``physical_mode_pin_rotate_offset`` is larger than zero, the pin index of ``pb_type`` (whose index is large than 1) will be shifted by the given offset. 
 
+    .. note:: If not defined, the default value of ``physical_mode_pin_rotate_offset`` is set to ``0``.
+
 .. note::
   It is highly recommended that only one physical mode is defined for a multi-mode configurable block. Try not to use nested physical mode definition. This will ease the debugging and lead to clean XML description.