Improved docstring for dynamic_delay_numpy module

lisainstrument/dynamic_delay_numpy.py

 """Functions for applying dynamic real-valued shifts to numpy arrays using Lagrange interpolation
 
-Use make_dynamic_shift_lagrange_numpy to create a Lagrange interpolator for numpy arrays.
+The main class in this module is DynamicShiftNumpy. It allows to perform a time-shifting
+opration on a numpy array, with time-dependent time shift. The main purpose of this
+class is for testing another class  lisainstrument.dynamic_delay_dask.DynamicShiftDask,
+which is equivalent but based on dask arrays instead numpy arrays. Both are supposed to
+yield exactly identical results.
+
+The interpolation method to be used is provided by the user in form of an object
+implementing the RegularInterpolator protocol defined in the module
+lisainstrument.regular_interpolators. This interpolation engine is based on numpy
+arrays. It is used both by DynamicShiftNumpy and DynamicShiftDask for the main work.
+The RegularInterpolator protocol is not responsible for setting up boundary conditions,
+which is the responsability of DynamicShiftNumpy (and DynamicShiftDask).
+
+The other parameters that determine the DynamicShiftNumpy behavior are collected
+in a class DynShiftCfg. It contains the left and right boundary conditions. The available
+options are defined by the ShiftBC enum class. DynShiftCfg also contains limits
+for the allowable minimum and maximum time shift. Those have to be supplied by the user
+because they cannot be determined from the data in DynamicShiftDask and DynamicShiftNumpy
+is required to behave exactly like DynamicShiftDask.
+
+The convenience functions make_dynamic_shift_lagrange_numpy() and
+make_dynamic_shift_linear_numpy() return a DynamicShiftNumpy instance
+employing Lagrange or linear interpolation, respectively.
+
+Example use:
+
+>>> op = make_dynamic_shift_lagrange_numpy(
+        order=31,
+        min_delay=-2., max_delay=21.,
+        left_bound=ShiftBC.FLAT, right_bound=ShiftBC.EXCEPTION
+    )
+>>> delay = np.linspace(-1.2,20.4,100)
+>>> data = np.linspace(0,1, len(delay)
+>>> shifted_data = op(data, -delay)
+
+
+Internally, the module works as follows. DynamicShiftNumpy contains a
+user-provided RegularInterpolator. The latter can interpolate to points
+within the given data, minus a margin size defined by RegularInterpolator
+implementations. Before calling RegularInterpolator, DynamicShiftNumpy
+extends the data by suitable margins filled according to the selected
+boundary conditions. The margin size is computed from the margins needed
+by the interpolator as well as the fixed limits specified for the timeshift.
 """
 
 from __future__ import annotations