added skip list documentation

tutorial/skip_list.md

@@ -0,0 +1,41 @@
+### Mini Tutorial for the Skip List class
+
+    1. skip_list<T> -- creates a skip list with T type elements.
+
+### **insert**:
+```cpp
+#include <algoplus/list.h>
+
+skip_list<int> s(3, 0.5);
+s.insert(10); // inserts 10 to the list.
+s.insert(5); // inserts 5 to the list.
+s.insert(13); // inserts 13 to the list.
+```
+
+### **remove**:
+```cpp
+#include <algoplus/list.h>
+
+skip_list<int> s(3, 0.5);
+s.insert(10); // inserts 10 to the list.
+s.insert(5); // inserts 5 to the list.
+s.insert(13); // inserts 13 to the list.
+
+s.remove(13); // removes 13 from the list.
+```
+
+### **search**:
+```cpp
+#include <algoplus/list.h>
+
+skip_list<int> s(3, 0.5);
+s.insert(10); // inserts 10 to the list.
+s.insert(5); // inserts 5 to the list.
+s.insert(13); // inserts 13 to the list.
+
+// returns true if the key is in the list.
+if(s.search(13)){
+    std::cout << "element 13 found in the list" << '\n';
+}
+
+```