docs(pilecore_tension): adding docstring for top_of_tension_zone_nap

Author: Pablo Vasconez

src/pypilecore/input/tension.py

@@ -105,6 +105,11 @@ def create_multi_cpt_payload(
             - Literal["surface"] (default).
                 In this case, the soil_properties.service_level
                 property is used.
+    top_of_tension_zone_nap:
+        The level [w.r.t. NAP] of the top of the tension zone from which the uplift capacity 
+        (tension) is calculated. If None, the top of the tension zone is set to the `pile_head_level_nap`.
+        Note that PileCore will automatically apply the remarks regarding L;a in CUR236 6.1.1. if
+        this standard is selected.
     excavation_depth_nap:
         Soil excavation depth after the CPT was taken. Unit: [m] w.r.t. NAP.
     excavation_param_t: