Adds link to new website in top bar

Author: spjuhel

doc/index.rst

@@ -135,3 +135,4 @@ specialized applications can be found in the `CLIMADA Petals
    Changelog <misc/CHANGELOG>
    CLIMADA Petals <https://climada-petals.readthedocs.io/en/stable/>
    WCR Group <https://wcr.ethz.ch/>
+   CLIMADA Website <https://climada.ethz.ch>