Update DIRECTORY.md with Strand Sort

Author: anaslimem

DIRECTORY.md

@@ -381,6 +381,7 @@
     * [Sleep Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/sleep_sort.rs)
     * [Sort Utils](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/sort_utils.rs)
     * [Stooge Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/stooge_sort.rs)
+    * [Strand Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/strand_sort.rs)
     * [Tim Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/tim_sort.rs)
     * [Tree Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/tree_sort.rs)
     * [Wave Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/wave_sort.rs)