Added text to state the Python version used to build the docs.

docs/src/_templates/footer.html

@@ -0,0 +1,5 @@
+{% extends "!footer.html" %}
+{% block extrafooter %}
+   Built using Python {{ python_version }}.
+   {{ super() }}
+{% endblock %}

docs/src/conf.py

@@ -95,9 +95,12 @@ def autolog(message):
 
 # Create a variable that can be inserted in the rst "|copyright_years|".
 # You can add more variables here if needed.
+
+build_python_version = ".".join([str(i) for i in sys.version_info[:3]])
+
 rst_epilog = f"""
 .. |copyright_years| replace:: 2010 - {upper_copy_year}
-.. |python_version| replace:: {'.'.join([str(i) for i in sys.version_info[:3]])}
+.. |python_version| replace:: {build_python_version}
 .. |iris_version| replace:: v{version}
 .. |build_date| replace:: ({datetime.datetime.now().strftime('%d %b %Y')})
 """
@@ -226,6 +229,7 @@ def autolog(message):
 
 html_context = {
     "copyright_years": "2010 - {}".format(upper_copy_year),
+    "python_version": build_python_version,
     # menu_links and menu_links_name are used in _templates/layout.html
     # to include some nice icons.  See http://fontawesome.io for a list of
     # icons (used in the sphinx_rtd_theme)

docs/src/developers_guide/contributing_documentation.rst

@@ -24,6 +24,9 @@ The documentation uses specific packages that need to be present.  Please see
 Building
 ~~~~~~~~
 
+This documentation is built using the latest Python version that Iris
+supports.  For more information see :ref:`installing_iris`.
+
 The build can be run from the documentation directory ``docs/src``.
 
 The build output for the html is found in the ``_build/html`` sub directory.

docs/src/installing.rst

@@ -17,7 +17,8 @@ any WSL_ distributions.
 .. _WSL: https://docs.microsoft.com/en-us/windows/wsl/install-win10
 
 .. note:: Iris currently supports and is tested against **Python 3.6** and
-          **Python 3.7**.
+          **Python 3.7**.  This documentation is built using a single
+          version of Python, version |python_version|.
 
 
 .. _installing_using_conda: