✏ add README

Graph/graph/README.md

+We propose to modelize a Non Directed Graph
+
+we must be able to:
+ * create a graph
+ * add nodes to this graph
+ * connect nodes with edges
+
+once this step is done we will implement to graph search algorithms:
+ * Depth First Search
+ * Breadth First Search
+
+I propose two graph implementation
+
+## The first implementation graph_1.py and main_1.py
+
+* *graph* store *nodes*
+* each *node* have an unique id and knows its neighbors
+
+## The second implementation graph_2.py and main_2.py
+
+* *graph* store nodes, and edges between nodes
+* *nodes* knows only its properties here, an unique id
+
+we see that the 2 search path algorithms *BFS* and *DFS* do not change whatever the graph implementation.
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