Document node attributes in titer model JSONs

Documents the specific attributes that get the custom prefix in titer
model node data JSON outputs and clarifies the use case for the
attribute prefix argument.

augur/titers.py

@@ -22,7 +22,7 @@ def register_parser(parent_subparsers):
     tree_model.add_argument('--titers', nargs='+', type=str, required=True, help="file with titer measurements")
     tree_model.add_argument('--tree', '-t', type=str, required=True, help="tree to perform fit titer model to")
     tree_model.add_argument('--allow-empty-model', action="store_true", help="allow model to be empty")
-    tree_model.add_argument('--attribute-prefix', default="", help="prefix for attributes in the JSON output")
+    tree_model.add_argument('--attribute-prefix', default="", help="prefix for node attributes in the JSON output including cumulative titer drop ('cTiter') and per-branch titer drop ('dTiter'). Set a prefix to disambiguate annotations from multiple tree model JSONs in the final Auspice JSON.")
     tree_model.add_argument('--output', '-o', type=str, required=True, help='JSON file to save titer model')
     tree_model.set_defaults(
         __command__ = infer_tree_model
@@ -34,7 +34,7 @@ def register_parser(parent_subparsers):
     sub_model.add_argument('--gene-names', nargs='+', type=str, required=True, help="names of the sequences in the alignment, same order assumed")
     sub_model.add_argument('--tree', '-t', type=str, help="optional tree to annotate fit titer model to")
     sub_model.add_argument('--allow-empty-model', action="store_true", help="allow model to be empty")
-    sub_model.add_argument('--attribute-prefix', default="", help="prefix for attributes in the JSON output")
+    sub_model.add_argument('--attribute-prefix', default="", help="prefix for node attributes in the JSON output including cumulative titer drop ('cTiterSub') and per-substitution titer drop ('dTiterSub'). Set a prefix to disambiguate annotations from multiple substitution model JSONs in the final Auspice JSON.")
     sub_model.add_argument('--output', '-o', type=str, required=True, help='JSON file to save titer model')
     sub_model.set_defaults(
         __command__ = infer_substitution_model