[doc] update clock network details

docs/source/manual/file_formats/clock_network.rst

@@ -187,6 +187,8 @@ Switch Point Settings
 The following syntax are applicable to the XML definition tagged by ``switch_point``.
 Note that a number of switch points can be defined under each clock spine ``spine``.
 
+.. note:: Use the coordinate of switch block to define switching points!
+
 .. option:: tap="<string>"
 
   Define which clock spine will be tapped from the current clock spine.
@@ -307,6 +309,8 @@ For example,
 
 where all the clock spines of the clock network ``clk_tree_0`` tap the clock pins ``clk`` of tile ``clb`` in a VPR architecture description file:
 
+.. note:: Use the name of ``subtile`` in the ``to_pin`` when there are a number of subtiles in your tile!
+
 .. code-block:: xml
 
   <tile name="clb">