fix comment on microsecond

xarray/coding/cftimeindex.py

@@ -135,9 +135,8 @@ def _parse_iso8601_with_reso(date_type, timestr):
     for attr in ["year", "month", "day", "hour", "minute", "second", "microsecond"]:
         value = result.get(attr, None)
         if value is not None:
-            # Note ISO8601 conventions allow for fractional seconds.
-            # TODO: Consider adding support for sub-second resolution?
             if attr == "microsecond":
+                # convert match string into valid microsecond value
                 value = 10 ** (6 - len(value)) * int(value)
             replace[attr] = int(value)
             resolution = attr