DOC: Fix intersphinx mapping and reference type

Author: effigies

Changelog

@@ -43,8 +43,8 @@ Enhancements
 ------------
 * Add :meth:`~nibabel.arrayproxy.ArrayProxy.copy` method to
   :class:`~nibabel.arrayproxy.ArrayProxy` (pr/1255) (CM, reviewed by Paul McCarthy)
-* Permit :meth:`~nibabel.xmlutils.XmlSerializable.to_xml` to pass keyword
-  arguments to :meth:`~xml.etree.ElementTree.tostring` (pr/1258)
+* Permit :meth:`~nibabel.xmlutils.XmlSerializable.to_xml` methods to pass keyword
+  arguments to :func:`xml.etree.ElementTree.tostring` (pr/1258)
   (CM)
 * Allow user expansion (e.g., ``~/...``) in strings passed to functions that
   accept paths (pr/1260) (Reinder Vos de Wael, reviewed by CM)

doc/source/conf.py

@@ -280,7 +280,12 @@
 
 
 # Example configuration for intersphinx: refer to the Python standard library.
-intersphinx_mapping = {'https://docs.python.org/3/': None}
+intersphinx_mapping = {
+    'python': ('https://docs.python.org/3', None),
+    'numpy': ('https://numpy.org/doc/stable', None),
+    'scipy': ('https://docs.scipy.org/doc/scipy', None),
+    'matplotlib': ('https://matplotlib.org/stable', None),
+}
 
 # Config of plot_directive
 plot_include_source = True