Clarify in docstrings that ScoringSystem is a literal string value

Author: TomHall2020

archeryutils/rounds.py

@@ -63,7 +63,7 @@ def at_target(  # noqa: PLR0913
         n_arrows : int
             number of arrows in this pass
         scoring_system : ScoringSystem
-            target face/scoring system type
+            Literal string value of target face/scoring system type.
         diameter : float or tuple of float, str
             Target diameter size (and units, default [cm])
         distance : float or tuple of float, str

archeryutils/targets.py

@@ -84,7 +84,8 @@ class Target:
     Parameters
     ----------
     scoring_system : ScoringSystem
-        target face/scoring system type. Must be one of the supported values.
+        Literal string value of target face/scoring system type.
+        Must be one of the supported values.
     diameter : float or tuple of float, str
         Target face diameter default [centimetres].
     distance : float or tuple of float, str