Added release note for shadow map light transforms

Documentation/release/dev/fix-shadowmap-light.md

+## Fix light transforms when computing shadow maps
+
+The `vtkShadowMapBakerPass` computes shadow maps for each light by simulating a `vtkCamera` for each
+light and compositing the rendered images. However, an unintentional side-effect of this was that
+the original light's transforms were being affected by this. In other words, the lights would be
+corrupt after the shadow map computation. To circumvent this, we cache the light
+transforms prior to the shadow map computation and then reset them after.
+
+![](http://vtk.org/files/ExternalData/SHA512/9412ed54080c7a972d786a269538a3dbd56a5aa070f2b35ba448dfd3cca211e7e4b4d196e07c8ff2d56ff4bb7b0855e5584758c09457d3d6f3c760ee47a4dded)