DOC: activate intersphinx extension

Author: pavoljuhas

doc/manual/source/conf.py

@@ -35,6 +35,7 @@
     'sphinx.ext.autodoc',
     'sphinx.ext.coverage',
     'sphinx.ext.napoleon',
+    'sphinx.ext.intersphinx',
 ]
 
 # Add any paths that contain templates here, relative to this directory.
@@ -266,4 +267,7 @@
 
 
 # Example configuration for intersphinx: refer to the Python standard library.
-# intersphinx_mapping = {'http://docs.python.org/': None}
+intersphinx_mapping = {
+    'numpy': ('https://docs.scipy.org/doc/numpy', None),
+    'python' : ('https://docs.python.org/3.7', None),
+}