Add the AdaCore logo on the doc

Also add an icon and update the background color of the table of content
title.

eng/libadalang/libadalang#1131

user_manual/conf.py

@@ -120,8 +120,11 @@
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.
-#html_theme_options = {}
-
+# https://sphinx-rtd-theme.readthedocs.io/en/stable/configuring.html#theme-options
+html_theme_options = {
+    # Use AdaCore blue in the Table Of Content
+    "style_nav_header_background": "#12284c",
+}
 # Add any paths that contain custom themes here, relative to this directory.
 #html_theme_path = []
 
@@ -134,12 +137,12 @@
 
 # The name of an image file (relative to this directory) to place at the top
 # of the sidebar.
-#html_logo = None
+html_logo = "adacore-logo-white.png"
 
 # The name of an image file (within the static path) to use as favicon of the
 # docs.  This file should be a Windows icon file (.ico) being 16x16 or 32x32
 # pixels large.
-#html_favicon = None
+html_favicon = "favicon.ico"
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,