Add 2021 on conferences page (#46)

Author: kaitlinnewson

_pages/code4lib-conference.md

@@ -12,6 +12,7 @@ legacy-date: 2006-02-23
 <p>Code4Lib conferences are subject to our community maintained <a href="https://github.com/code4lib/antiharassment-policy/blob/master/code_of_conduct.md">CodeofConduct4Lib</a>
 
 <ul>
+    <li><a href="/conference/2021/">code4lib 2021</a> - Online. March 22-26. See the <a href="https://2021.code4lib.org/">2021 conference website</a>.</li>
     <li><a href="/conference/2020/">code4lib 2020</a> - Pittsburgh, PA. March 8-11. See the <a href="https://2020.code4lib.org/">2020 conference website</a>.</li>
     <li><a href="/conference/2019/">code4lib 2019</a> - San José, CA. February
     19-22. See the <a href="https://2019.code4lib.org/">2019 conference website</a>.</li>