Update related links in footer section

Author: yasulab

_config.yml

@@ -8,6 +8,7 @@ link_to_youtube:  https://youtube.com/@DojoConJapan
 link_to_twitter:  https://twitter.com/DojoConJapan
 link_to_facebook: https://facebook.com/DojoConJapan
 link_to_github:   https://github.com/coderdojo-japan/dojocon.coderdojo.jp
+link_to_decadojo: https://decadojo.coderdojo.jp
 link_to_privacy:  https://coderdojo.jp/privacy
 copyright: DojoCon Japan & <a href='https://coderdojo.jp/'>CoderDojo Japan</a>
 

index.html

@@ -321,6 +321,7 @@ <h3 class="headline">
 	    <a href='{{ site.link_to_twitter  }}'>Twitter</a> |
 	    <a href='{{ site.link_to_youtube  }}'>YouTube</a> |
 	    <a href='{{ site.link_to_github   }}'>GitHub</a> |
+	    <a href='{{ site.link_to_decadojo }}'>DecaDojo</a> |
 	    <a href='{{ site.link_to_privacy  }}'>Privacy</a>
 	  </p>
 	</div><!-- END #footer_bottom_inner -->