Add a newline to the hello, world! example to avoid confusion

[douxxtech]

First of all, thanks for those posts that explain very well the language! I'm new to it and still have a lot to learn, but this is a great introduction.

Description
While trying to run the provided hello world snippet, I ran into an issue: the code compiled correctly, but no hello, world! was displayed when run.

I think it might be related to my bash prompt, but I can't confirm that.
Adding a newline character (LF, ASCII 10) at the end of the string fixed the issue:

Here are the snippets I edited in this PR:

;; Definition of the `data` section
section .data
        ;; String variable with the value `hello world!`. 
        ;; `10` is the ASCII code for the line feed character (LF), i.e., '\n'.
        msg db "hello, world!", 10 ; <- addition here and in the comment

        ;; Set the third argument of `sys_write` to the length of the `msg` variable's value (14 bytes).
        mov rdx, 14 ; edited the bytes count to match the new one

Changes proposed in this pull request:

• Add a newline character to the hello, world! example

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Additionally, I saw that you're using ;; for comments in all of your code snippets, but the language seems to only require one (;). Is it some sort of convention?

[0xAX]

@douxxtech thank you for PR!