update readme & added image

Author: Dentrax

linked-list-find-length/README.md

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+<h1 align="center">LinkedList Find Length Source</h1>
+
+[What It Is](#what-it-is)
+
+## What It Is
+
+For example, the function should return 5 for linked list `[1 -> 3 -> 1 -> 2 -> 1]`
+
+![Preview Thumbnail](https://raw.githubusercontent.com/Dentrax/Data-Structures-with-Go/master/linked-list-find-length/resources/find-length.png)
+
+
+METHOD 1 (Iterative Solution)
+--------------------------
+
+* 1) Initialize count as 0 
+* 2) Initialize a node pointer, current = head.
+* 3) Do following while current is not NULL
+     a) current = current -> next
+     b) count++;
+* 4) Return count 
+
+> * Input: Linked List = `[1 -> 3 -> 1 -> 2 -> 1]`
+> * Output: count of nodes is `5`
+
+**Algorithm Complexity**
+
+| Complexity		| Notation  |
+| ----------------- |:---------:|
+| `Time Complexity`	| `O(n)`    |