Add iostream and initialization

ch_1/iostream/main.cpp

@@ -0,0 +1,16 @@
+#include <iostream>
+
+int main() {
+    std::cout << "Hello, world!\n";
+
+    double pi { 3.1415 };
+    std::cout << "pi is approximately " << pi << std::endl;
+
+    std::cout << "Enter a character: ";
+    char c { };
+    std::cin >> c;
+
+    std::cout << "You entered " << c << "\n";
+    
+    return 0;
+}