Hello World with argument

Hello World with argument

This will simply print "Hello, " followed by the first argument from the
commandline.

Every Haskell program needs to have a main "action" in the Main module.
This is the entry point.

Files starting with `module <Foo>` will be part of the `Foo` module.

By convention modules are capitalized and definitions aren't.

`import System.Environment` provides `getArgs` to access cli arguments.

Haskell is strongly typed and types may be assigned with `::`. In this case
`main` is of type `IO ()` which is an IO action holding no information.
(more on that later hopefully, as I don't fully understand that.)