chore: fix readme and add jackolantern program

Jack-O'-Lantern-Juxtaposition/main.cpp

@@ -0,0 +1,9 @@
+#include <iostream>
+using namespace std;
+
+int main(){
+    int x, y, z;
+    cin >> x >> y >> z;
+    cout << x*y*z << endl;
+    return 0;
+}

README.md

@@ -4,12 +4,12 @@
 
 ## System requirements
 
-- A C++ compiler such as GCC
+- A C++ compiler such as G++ (should come with GCC)
 
 ## Development
 
 - edit the `main.cpp` files in each folder
-- run `gcc` on them
+- run `g++` on them
 - if no arguemnts, run `./a.out` to run the program
 
 ## License