Document optional distinct function

Author: thekid

README.md

@@ -100,7 +100,7 @@ The following operations return a new `Sequence` instance on which more intermed
 * **peek** - Calls a function for each element in the sequence; especially useful for debugging, e.g. `peek('var_dump', [])`.
 * **counting** - Increments the integer given as its argument for each element in the sequence.
 * **flatten** - Flattens sequences inside the sequence and returns a new list containing all values from all sequences.
-* **distinct** - Returns a new sequence which only consists of unique elements. Uniqueness is calculated using the `util.Objects::hashOf()` method.
+* **distinct** - Returns a new sequence which only consists of unique elements. Uniqueness is calculated using the `util.Objects::hashOf()` method by default (*but can be passed another function*).
 * **sorted** - Returns a sorted collection. Can be invoked with a comparator function, a `util.Comparator` instance or the sort flags from PHP's sort() function (e.g. `SORT_NUMERIC | SORT_DESC`).
 
 Terminal operations