theme.conf root_icon and root_icon_alt_text variables interpolated in…

… layout.html

This fixes a partial integration of root_icon and adds the new variable root_icon_alt_text

python_docs_theme/layout.html

@@ -14,7 +14,7 @@ <h3>{{ _('Navigation') }}</h3>
           </li>
           {%- endfor %}
           {%- block rootrellink %}
-          <li><img src="{{ pathto('_static/' + theme_root_icon, 1) }}" alt="python logo" style="vertical-align: middle; margin-top: -1px"/></li>
+          <li><img src="{{ pathto('_static/' + theme_root_icon, 1) }}" alt="{{theme_root_icon_alt_text}}" style="vertical-align: middle; margin-top: -1px"/></li>
           <li><a href="{{theme_root_url}}">{{theme_root_name}}</a>{{ reldelim1 }}</li>
           <li class="switchers">
             <div class="language_switcher_placeholder"></div>
@@ -100,7 +100,7 @@ <h3>{{ _('Navigation') }}</h3>
         </label>
         <span class="nav-items-wrapper">
             <a href="{{ theme_root_url }}" class="nav-logo">
-                <img src="{{ pathto('_static/' + theme_root_icon, 1) }}" alt="Logo"/>
+                <img src="{{ pathto('_static/' + theme_root_icon, 1) }}" alt="{{theme_root_icon_alt_text}}"/>
             </a>
             <span class="version_switcher_placeholder"></span>
             {%- if pagename != "search" and builder != "singlehtml" %}

python_docs_theme/theme.conf

@@ -32,4 +32,5 @@ root_name = Python
 root_url = https://www.python.org/
 root_icon = py.svg
 root_include_title = True
+root_icon_alt_text = Python Logo
 copyright_url =