Update DIRECTORY.md

Author: DenizAltunkapan

DIRECTORY.md

@@ -488,6 +488,7 @@
           - 📄 [Volume](src/main/java/com/thealgorithms/maths/Volume.java)
         - 📁 **matrix**
           - 📄 [InverseOfMatrix](src/main/java/com/thealgorithms/matrix/InverseOfMatrix.java)
+          - 📄 [MatrixMultiplication](src/main/java/com/thealgorithms/matrix/MatrixMultiplication.java)
           - 📄 [MatrixRank](src/main/java/com/thealgorithms/matrix/MatrixRank.java)
           - 📄 [MatrixTranspose](src/main/java/com/thealgorithms/matrix/MatrixTranspose.java)
           - 📄 [MedianOfMatrix](src/main/java/com/thealgorithms/matrix/MedianOfMatrix.java)
@@ -1177,6 +1178,7 @@
             - 📄 [PrimeFactorizationTest](src/test/java/com/thealgorithms/maths/prime/PrimeFactorizationTest.java)
         - 📁 **matrix**
           - 📄 [InverseOfMatrixTest](src/test/java/com/thealgorithms/matrix/InverseOfMatrixTest.java)
+          - 📄 [MatrixMultiplicationTest](src/test/java/com/thealgorithms/matrix/MatrixMultiplicationTest.java)
           - 📄 [MatrixRankTest](src/test/java/com/thealgorithms/matrix/MatrixRankTest.java)
           - 📄 [MatrixTransposeTest](src/test/java/com/thealgorithms/matrix/MatrixTransposeTest.java)
           - 📄 [MatrixUtilTest](src/test/java/com/thealgorithms/matrix/MatrixUtilTest.java)