Add ESModel to docs + tweak docstring

docs/api_reference.md

@@ -17,6 +17,9 @@ Each type of model is contained in a separate Python class (with name ending in
 ## DCMModel
 ::: echosms.DCMModel
 
+## ESModel
+::: echosms.ESModel
+
 ## ReferenceModels
 Reference models are the models and parameters defined in the Jech et al, 2015 paper. The parameters are stored in a TOML-formatted file in the echoSMs repository and the ``ReferenceModels`` class provides easy access to the data in that file. 
 

src/echosms/esmodel.py

@@ -12,8 +12,7 @@
 class ESModel(ScatterModelBase):
     """Elastic sphere (ES) scattering model.
 
-    This class calculates acoustic scatter from spheres and shells with various
-    boundary conditions, as listed in the ``boundary_types`` class attribute.
+    This class calculates acoustic scatter from elastic spheres.
     """
 
     def __init__(self):
@@ -34,9 +33,9 @@ def calculate_ts_single(self, medium_c, medium_rho, diameter, theta, f, boundary
         Parameters
         ----------
         medium_c : float
-            Sound speed in the fluid medium surrounding the target [m/s].
+            Sound speed in the fluid medium surrounding the sphere [m/s].
         medium_rho : float
-            Density of the fluid medium surrounding the target [kg/m³].
+            Density of the fluid medium surrounding the sphere [kg/m³].
         diameter : float
             Diameter of the sphere [m].
         theta : float