add Docs link

Author: njzjz

docs/.vuepress/config.js

@@ -26,6 +26,7 @@ module.exports = {
                 navbar: [
                     { text: 'Home', link: '/' },
                     { text: 'Blog', link: '/blog/', target: '_blank' },
+                    { text: 'Docs', link: 'https://docs.deepmodeling.org/', target: '_blank' },
                 ]
             },
         }