add readme for insertion sort

sorting_algorithms/insertion_sort/README.md

@@ -0,0 +1,17 @@
+# Insertion sort
+
+![insertion1](https://upload.wikimedia.org/wikipedia/commons/4/42/Insertion_sort.gif)
+
+[read more in wikipedia](https://en.wikipedia.org/wiki/Insertion_sort)
+
+Insertion sort is a simple sorting algorithm that builds the final sorted array (or list) one item at a time. It is much less efficient on large lists than more advanced algorithms such as quicksort, heapsort, or merge sort. However, insertion sort provides several advantages:
+
+- Simple implementation: Jon Bentley shows a three-line C version, and a five-line optimized version
+- Efficient for (quite) small data sets, much like other quadratic sorting algorithms
+- More efficient in practice than most other simple quadratic (i.e., O(n2)) algorithms such as selection sort or bubble sort
+- Adaptive, i.e., efficient for data sets that are already substantially sorted: the time complexity is O(kn) when each element in the input is no more than k places away from its sorted position
+- Stable; i.e., does not change the relative order of elements with equal keys
+- In-place; i.e., only requires a constant amount O(1) of additional memory space
+- Online; i.e., can sort a list as it receives it
+
+When people manually sort cards in a bridge hand, most use a method that is similar to insertion sort.