docs: mention custom sorting (#10812)

doc/docs.md

@@ -889,6 +889,40 @@ mut users := [User{21, 'Bob'}, User{20, 'Zarkon'}, User{25, 'Alice'}]
 users.sort(a.age < b.age) // sort by User.age int field
 users.sort(a.name > b.name) // reverse sort by User.name string field
 ```
+V also supports custom sorting, through the `sort_with_compare` array method.
+Which expects a comparing function which will define the sort order.
+Useful for sorting on multiple fields at the same time by custom sorting rules.
+The code below sorts the array ascending on `name` and descending `age`.
+```v
+struct User {
+	age  int
+	name string
+}
+
+mut users := [User{21, 'Bob'}, User{65, 'Bob'}, User{25, 'Alice'}]
+
+custom_sort_fn := fn (a &User, b &User) int {
+	// return -1 when a comes before b
+	// return 0, when both are in same order
+	// return 1 when b comes before a
+	if a.name == b.name {
+		if a.age < b.age {
+			return 1
+		}
+		if a.age > b.age {
+			return -1
+		}
+		return 0
+	}
+	if a.name < b.name {
+		return -1
+	} else if a.name > b.name {
+		return 1
+	}
+	return 0
+}
+users.sort_with_compare(custom_sort_fn)
+```
 
 #### Array Slices