Add 'Contribute' to side nav bar

Author: Qianqianye

src/templates/partials/sidebar.hbs

@@ -18,6 +18,7 @@ slug: sidebar
       <li><a href="{{root}}/learn/">{{#i18n "Learn"}}{{/i18n}}</a></li>
       <li><a href="{{root}}/teach/">{{#i18n "Teach"}}{{/i18n}}</a></li>
       <li><a href="{{root}}/examples/">{{#i18n "Examples"}}{{/i18n}}</a></li>
+      <li><a href="https://p5js.org/contributor-docs/#/">{{#i18n "Contribute"}}{{/i18n}}</a></li>
       <li><a href="{{root}}/books/">{{#i18n "Books"}}{{/i18n}}</a></li>
       <li><a href="{{root}}/community/">{{#i18n "Community"}}{{/i18n}}</a></li>
       <li><a href="https://showcase.p5js.org">{{#i18n "Showcase"}}{{/i18n}}</a></li>