Merge branch 'typo-and' into 'master'

Fix typo

See merge request !20

README.rst

@@ -186,7 +186,7 @@ This requires passing configuration to AlekSIS itself.
        --set aleksis.config.2fa.enabled=true \
        --set aleksis.config.2fa.yubikey.enabled=true
 
-Upgrade and existing deployment
+Upgrade an existing deployment
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 In order to upgrade an existing deployment, care has to be taken to pass