Documentation: Add in section about TreeGrid column types

doc/source/using-as-a-library.rst

@@ -205,6 +205,15 @@ once it is fully populated.  In either case, a visitor method will be required.
 should accept a :py:class:`~volatility.framework.interfaces.renderers.TreeNode` and an `accumulator`.  It will
 return an updated accumulator.
 
+When provided a :py:class:`~volatility.framework.interfaces.renderers.TreeNode`, it can be accessed as a dictionary
+based on the column names that the treegrid contains.  It should be noted that each column can contain only the
+type specified in the `column.type` field (which can be a simple type like string, integer, float, bytes or
+a more complex type, like a DateTime, a Disassembly or a descendent of
+:py:class:`~volatility.framework.interfaces.renderers.BaseAbsentValue`).  The various fields may also be wrapped in
+`format_hints` designed to tell the user interface how to render the data.  These hints can be things like Bin, Hex or
+HexBytes, so that fields like offsets are displayed in hex form or so that bytes are displayed in their hex form rather
+than their raw form.
+
 A simple text renderer (that returns output immediately) would appear as follows.  This doesn't use
 the accumulator, but instead uses print to directly produce the output.  This is not recommended: