IVGCVSW-1804 : add subtraction layer to the public interface

Change-Id: I2c1b622b5199000c01af387bb994267c2b91f89c
diff --git a/include/armnn/INetwork.hpp b/include/armnn/INetwork.hpp
index be03f83..0405074 100644
--- a/include/armnn/INetwork.hpp
+++ b/include/armnn/INetwork.hpp
@@ -274,6 +274,11 @@
     /// @return - Interface for configuring the layer.
     virtual IConnectableLayer* AddDivisionLayer(const char* name = nullptr) = 0;
 
+    /// Adds a subtraction layer to the network.
+    /// @param name - Optional name for the layer.
+    /// @return - Interface for configuring the layer.
+    virtual IConnectableLayer* AddSubtractionLayer(const char* name = nullptr) = 0;
+
 protected:
     ~INetwork() {}
 };