Add alt text for TOTP setup QR code

Part of #32.

spongeauth/templates/twofa/setup/totp.html

@@ -16,7 +16,7 @@ <h4 class="panel-title">{% trans "Secure your account" %}</h4>
                     <ol>
                         <li>
                             <p>{% trans "Scan the QR code below to add Sponge to your authenticator." %}</p>
-                            <p class="text-center"><img src="data:image/svg+xml;utf8,{{ qr_code_svg|urlencode:"" }}"></p>
+                            <p class="text-center"><img src="data:image/svg+xml;utf8,{{ qr_code_svg|urlencode:"" }}" alt="TOTP Authenticator QR Code for secret {{ b32_secret }}"></p>
                         </li>
                         <li>
                             {% trans "Enter the 6 digit code that it displays to verify that your authenticator is set up correctly. You'll need to do this every time you log in from now on." %}

spongeauth/twofa/views.py

@@ -148,7 +148,7 @@ def setup_totp(request):
             messages.success(request, _('Your authenticator has been added to your account.'))
             return _generate_paper_codes_if_needed(request.user, reverse('twofa:list'))
 
-    return render(request, 'twofa/setup/totp.html', {'form': form, 'qr_code_svg': img_buf.getvalue()})
+    return render(request, 'twofa/setup/totp.html', {'form': form, 'qr_code_svg': img_buf.getvalue(), 'b32_secret': b32_secret})
 
 
 @login_required