Add xtensor cross references in Numpy cheat sheet

Author: AntoinePrv

docs/source/conf.py

@@ -45,4 +45,5 @@ def setup(app):
 intersphinx_mapping = {
     "numpy": ("https://numpy.org/doc/stable/", None),
     "scipy": ("https://docs.scipy.org/doc/scipy/reference", None),
+    "xtensor-blas": ("https://xtensor-blas.readthedocs.io/en/stable", None),
 }