add how to use

README.md

 # CIFAR10 Loader written in C++
+
+## Requirement
+
+- C++11
+
+## Use
+
+```cpp
+const auto cifar_10_sample = mtk::load_cifar_10("cifar-10-batches-bin/data_batch_1.bin");
+for(const auto& sample : cifar_10_sample){
+
+	// type : std::vector<unsigned int>(32 x 32)
+	// unsigned int <- 0xrrggbb
+	const auto image = std::get<0>(sample);
+
+	// type : int
+	const auto label = std::get<1>(sample);
+}
+```