add Chapter18

Chapter18/cib/libs/flow/run.hpp

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+#pragma once
+
+#include <cib/built.hpp>
+#include <flow/common.hpp>
+
+namespace flow {
+/**
+ * Run the flow given by 'Tag'.
+ *
+ * @tparam Tag Type of the flow to be ran. This is the name of the flow::builder
+ * used to declare and build the flow.
+ */
+template <typename Tag> FunctionPtr &run = cib::service<Tag>;
+} // namespace flow