add a complete description

DESCRIPTION

@@ -5,7 +5,12 @@ Authors@R: c(
     person("Daniel", "Falbel", email = "[email protected]", role = c("aut", "cre", "cph")),
     person(family = "RStudio", role = c("cph"))
     )
-Description: What the package does (one paragraph).
+Description: A high level interface for 'torch' providing utilities to reduce the
+    the amount of code needed for common tasks, abstract away torch details and 
+    make the same code work on both the 'CPU' and 'GPU'. It's flexible enough to
+    support expressing a large range of models. It's heavily inspired by 'fastai' by 
+    Howard et al. (2020) <arXiv:2002.04688>, 'Keras' by Chollet et al. (2015) and 
+    'Pytorch Lightning' by Falcon et al. (2019) <doi:10.5281/zenodo.3828935>.
 License: MIT + file LICENSE
 URL: https://mlverse.github.io/luz, https://github.com/mlverse/luz
 Encoding: UTF-8