Add LZW and Arithmetic Coding algorithms in compression category

Author: enqneres

src/main/java/com/thealgorithms/compression/ArithmeticCoding.java

@@ -2,6 +2,11 @@
 
 import java.util.Map;
 
+/**
+ * Implementation of Arithmetic Coding algorithm.
+ * Reference: https://en.wikipedia.org/wiki/Arithmetic_coding
+ */
+
 public class ArithmeticCoding {
 
     public static double encode(String input, Map<Character, Double> probabilities) {

src/main/java/com/thealgorithms/compression/LZW.java

@@ -2,6 +2,11 @@
 
 import java.util.*;
 
+/**
+ * Implementation of LZW (Lempel–Ziv–Welch) compression algorithm.
+ * Reference: https://en.wikipedia.org/wiki/Lempel–Ziv–Welch
+ */
+
 public class LZW {
 
     public static List<Integer> compress(String input) {