tweak copy

Based on feedback here https://github.com/NHSDigital/manage-breast-screening-prototype/pull/239/changes/BASE..8eaa5f7dce95236beaf5396df222112dd9b37cb9#diff-9e9682ef84095bb32c79601ae3a8b063b39e0a616c245f46431988c5bdc0e4fe

Author: MatMoore

manage_breast_screening/mammograms/forms/other_information/pregnancy_and_breastfeeding_form.py

@@ -54,7 +54,7 @@ def __init__(self, *args, participant, **kwargs):
         self.fields["approx_breastfeeding_start_date"] = CharField(
             required=False,
             label="Approximate date started",
-            hint=f"For example, since {format_relative_months(-2)}",
+            hint=f"For example, {format_relative_months(-2)}",
             error_messages={
                 "required": "Provide details of when they started breastfeeding"
             },