doc: adds todo note for later

tantri/dipoles/__init__.py

@@ -31,6 +31,9 @@ class Dipole:
 	w: float
 
 	# For caching purposes tell each dipole where the dots are
+	# TODO: This can be done better by only passing into the time series the non-repeated p s and w,
+	#     and then creating a new wrapper type to include all the cached stuff.
+	#     Realistically, the dot positions and measurement type data should live in the time series.
 	dot_positions: typing.Sequence[DotPosition]
 
 	measurement_type: DipoleMeasurementType