Update README.md

Add a note about always open/closed shcedules

README.md

@@ -467,7 +467,6 @@ Set `$cap` to a date so if no open time can be found before this moment, `$cap`
 ```php
 $openingHours->nextOpen(new DateTime('2016-12-24 11:00:00'));
 ```
-`
 
 #### `OpeningHours::nextClose`
 
@@ -487,6 +486,11 @@ Set `$searchUntil` to a date to throw an exception if no closed time can be foun
 
 Set `$cap` to a date so if no closed time can be found before this moment, `$cap` is returned.
 
+If the schedule is always open or always closed, there is no state change to found and therefore
+`nextOpen` (but also `previousOpen`, `nextClose` and `previousClose`) will throw a `MaximumLimitExceeded`
+You can catch it and react accordingly or you can use `isAlwaysOpen` / `isAlwaysClosed` methods
+to anticipate such case.
+
 ```php
 $openingHours->nextClose(new DateTime('2016-12-24 11:00:00'));
 ```