Change docs header link to VirtualShip website (#208)

Change link in docs header from Parcels website to VirtualShip website.

Author: j-atkins

docs/index.md

@@ -8,7 +8,7 @@ Home <self>
 user-guide/index
 api/index
 contributing/index
-OceanParcels <https://oceanparcels.org>
+VirtualShip Website <https://virtualship.oceanparcels.org/>
 ```
 
 ```{include} ../README.md