update NEWS.md

Author: ufechner7

NEWS.md

@@ -4,4 +4,5 @@ This project is based on version 1.0 of the Python project [Vortex-Step-Method](
 ## Noteworthy Differences
 - implemented in Julia, therefore about 20 times faster
 - an importer for `.obj` wing geometry files was added (see: [#10](https://github.com/Albatross-Kite-Transport/VortexStepMethod.jl/issues/10))
-- a ram-air kite example was added
+- a ram-air kite example was added
+- `Umag` was replaced with `v_a` as variable name for the norm of the apparent wind speed