Adding parabolic term description to NEWS.md (#1207)

NEWS.md

@@ -9,6 +9,22 @@ for human readability.
 
 #### Added
 
+- Experimental support for 2D parabolic diffusion terms has been added.
+  * `LaplaceDiffusion2D` and `CompressibleNavierStokesDiffusion2D` can be used to add
+  diffusion to systems. `LaplaceDiffusion2D` can be used to add scalar diffusion to each
+  equation of a system, while `CompressibleNavierStokesDiffusion2D` can be used to add
+  Navier-Stokes diffusion to `CompressibleEulerEquations2D`.
+  * Parabolic boundary conditions can be imposed as well. For `LaplaceDiffusion2D`, both
+  `Dirichlet` and `Neumann` conditions are supported. For `CompressibleNavierStokesDiffusion2D`,
+  viscous no-slip velocity boundary conditions are supported, along with adiabatic and isothermal
+  temperature boundary conditions. See the boundary condition container
+  `BoundaryConditionNavierStokesWall` and boundary condition types `NoSlip`, `Adiabatic`, and
+  `Isothermal` for more information.
+  * `CompressibleNavierStokesDiffusion2D` can utilize both primitive variables (which are not
+  guaranteed to provably dissipate entropy) and entropy variables (which provably dissipate
+  entropy at the semi-discrete level).
+  * Please check the `examples` directory for further information about the supported setups.
+    Further documentation will be added later.
 - Numerical fluxes `flux_shima_etal_turbo` and `flux_ranocha_turbo` that are
   equivalent to their non-`_turbo` counterparts but may enable specialized
   methods making use of SIMD instructions to increase runtime efficiency