Issue #5: Add StrategicPointMenu scene in scenes folder

[Sop-S]

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[davcri]

Thanks for your pull request @Sop-S! I just merged it into master.

The strategic point menu is fine!

Also I noticed that I didn't write any convention about node names in the README, I'm going to do it.
I like using CamelCase style for node names because it's easier to reference nodes via GDScript. When using the dollar operator you can simply type $SlotTopLeft to get a reference to that node, but using the dash symbol in the node name forces you to write $"slot-top-left" using the quotes.

[davcri]

@Sop-S I just added your username to the credits.gd script, so that your username will appear in the game credits! If you don't want to appear, or if you want to change the displayed name just let me know.