Update docs/upgrade.md

Co-authored-by: Francesco Giudici <francesco.giudici@suse.com>
Signed-off-by: Itxaka <igarcia@suse.com>

docs/upgrade.md

@@ -8,7 +8,7 @@ to use Kubernetes approaches to upgrade the components.
 Elemental Teal is upgraded with the Elemental operator. Refer to the
 [Elemental Operator](https://github.com/rancher/elemental-operator/blob/main/README.md) documentation for complete information.
 
-There is two ways of selecting nodes for upgrading. Via a cluster target, which will match ALL nodes in a cluster that matches our
+There are two ways of selecting nodes for upgrading. Via a cluster target, which will match ALL nodes in a cluster that matches our
 selector or via node selector, which will match nodes based on the node labels. Node selecter allows us to be more targeted with the upgrade
 while cluster selector just select all the nodes in a matched cluster.