Add pyam intersphinx

conf.py

@@ -27,7 +27,9 @@
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = []
+extensions = [
+    "sphinx.ext.intersphinx",
+]
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ["_templates"]
@@ -37,6 +39,12 @@
 # This pattern also affects html_static_path and html_extra_path.
 exclude_patterns = []
 
+# -- Intersphinx -------------------------------------------------------------
+
+# Intersphinx configuration.
+intersphinx_mapping = {
+    "pyam": ("https://pyam-iamc.readthedocs.io/en/stable/", None),
+}
 
 # -- Options for HTML output -------------------------------------------------