Tweak wording of Rachio options (#42849)

This is a bit clearer to my eyes.

homeassistant/components/rachio/strings.json

@@ -22,7 +22,7 @@
     "step": {
       "init": {
         "data": {
-          "manual_run_mins": "For how long, in minutes, to turn on a station when the switch is enabled."
+          "manual_run_mins": "Duration in minutes to run when activating a zone switch"
         }
       }
     }

homeassistant/components/rachio/translations/en.json

@@ -22,7 +22,7 @@
         "step": {
             "init": {
                 "data": {
-                    "manual_run_mins": "For how long, in minutes, to turn on a station when the switch is enabled."
+                    "manual_run_mins": "Duration in minutes to run when activating a zone switch"
                 }
             }
         }