Update README.md

README.md

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+# Argument Parser
+
+## Simple Arguments
+
+```cpp
+#include <argparse.hpp>
+
+int main(int argc, char *argv[]) {
+  argparse::ArgumentParser program("main");
+  
+  program.add_argument("config")
+    .help("configuration file")
+    .default_value([]() { return "config.yml" });
+    
+  program.add_argument("n", "-n", "--num_iterations")
+    .help("The list of input files")
+    .action([](const std::string& value) { return std::stoi(value); });
+    
+  program.parse(argc, argv);
+  std::string config = program.get("config");
+  int num_iterations = program.get<int>("n");  
+  
+  return 0;
+}
+```
+
+## Parsing a list of arguments
+
+```cpp
+#include <argparse.hpp>
+
+int main(int argc, char *argv[]) {
+  argparse::ArgumentParser program("main");
+  
+  program.add_argument("--input_files")
+    .help("The list of input files")
+    .nargs(3);
+    
+  program.parse(argc, argv);
+  std::vector<std::string> files = program.get<std::vector<std::string>>("--input_files");  
+  
+  return 0;
+}
+```