Modernise SKC docs theme

Author: stackhpc-ci

doc/requirements.txt

@@ -3,3 +3,4 @@ sphinx-copybutton # MIT
 sphinx-substitution-extensions # MIT
 sphinx>=4.2.0 # BSD
 sphinxcontrib-svg2pdfconverter>=0.1.0 # BSD
+furo # MIT

doc/source/conf.py

@@ -89,7 +89,7 @@
 # The theme to use for HTML and HTML Help pages.  Major themes that come with
 # Sphinx are currently 'default' and 'sphinxdoc'.
 # html_theme_path = []
-html_theme = 'default'
+html_theme = 'furo'
 # html_static_path = ['static']
 
 # Add any paths that contain "extra" files, such as .htaccess or