Update README.md

README.md

-Convertor from xBEL to CellDesigner.
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+Convertor from xBEL to CellDesigner.
+ Input : .XBEL file (to be provided)
+        several mapping files already provided, can be updated to include any user defined entity mapping
+ Output : nodes.txt (nodes with anotation and location information)
+        reactions.txt (reactions, with nodes referring to nodes.txt and annotation)
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