clarify whatsnew for modes

doc/source/whatsnew/0.3.rst

@@ -123,14 +123,16 @@ containing all the parameters as attributes::
 Arguments can be passed in an equivalent way in calls to
 `~kwant.solvers.default.wave_function` and `~kwant.solvers.default.ldos`.
 
-Change of modes format and `~kwant.builder.ModesLead`
------------------------------------------------------
-The return format of the modes calculation was simplified, and so was
-the information required by the solvers about the leads.
+Calculation of modes separated from solving
+-------------------------------------------
+The interface that solvers expect from leads attached to a
+`~kwant.system.FiniteSystem` has been simplified and codified (see there).
+Similar to self-energy, calculation of modes is now the lead's own
+responsibility.
+
+The new class `~kwant.builder.ModesLead` allows to attach leads that have a
+custom way of calculating their modes (e.g. ideal leads) directly to a
+`~kwant.builder.Builder`.
 
 `~kwant.physics.selfenergy` now uses the output of `~kwant.physics.modes` as
 input instead of the slice Hamiltonian and inter-slice hopping.
-
-Similar to self-energy, calculation of modes is now the lead's responsibility.
-There is also a new object `~kwant.builder.ModesLead`, allowing to attach leads
-that have a custom way of calculating their modes, e.g. ideal leads.