chore: remove trailing whitespace from README.md formatting

examples/21_DoWhile.java

@@ -0,0 +1,21 @@
+public class DoWhile {
+    public static int main() {
+        int i = 0;
+        int sum = 0;
+
+        do {
+            sum = sum + i;
+            i = i + 1;
+        } while (i < 5);
+
+        System.out.println(sum);
+
+        int j = 10;
+        do {
+            System.out.println(j);
+            j = j - 1;
+        } while (j > 7);
+
+        return 0;
+    }
+}