Add simple use example

[librasteve]

The problem

Recently on the Discord beginner channel, a user was confused by the detailed Package / Module features and documentation

Solution provided

Create a minimal example to declare and call a class in an external file in the same dir.

[lizmat]

Feels like at this point, it should also be mentioned (or at least referred to) on setting up a module for proper installation, and tools such as App::Mi6

[librasteve]

@lizmat - I certainly get the point of Mi6 ... but I feel that this is a tool for those that want to make a module and that are reading the relevant docs page already - which may be one of these:

for example in the Introductory section we have:
https://docs.raku.org/language/modules <=== here be the gold
https://docs.raku.org/language/module-packages
https://docs.raku.org/language/modules-extra

and then in the Reference section we have:
https://docs.raku.org/language/module-packages

don't know if you watch raku-beginner - I am just taking a whiney person at face value - and yet agreeing that the minimal variant of use should be set out somewhere

the '101' somewhere that we chose is actually imo a backwater so this PR is not going to be too helpful to the casual arriver

actually calling subs from another file is a bit odd - but I tried to be nice and not push back on that since I know raku is very lightweight for this kind of thing

[librasteve]

@lizmat, I see that I have been unable to convince you that this PR is a standalone minimal example for beginners who care about splitting code over multiple files --- my comment about is to try and separate this PR from the wider wiork that needs doing for package/module docs in general and I believe that referencing how to build a module (with Mi^ or any other way) doesn't belong here

I hope that you will come to see that adding in references to "how to build a module" pages reduces the simplicity, brevity and purity of raku in "minimal multi file mode" and urge you to allow this merge forward as written - or at least relent on the basis that the perfect (wider project on improving modules docs) is the enemy of the good (this short response to a newb concern)

or, feel free to make changes if you prefer

either way, please comment here and I will close this PR either way

[coke]

:lang<shell> so we don't try to compile it

[coke]

To address @lizmat's concern, maybe we can note this is intended to be a simplistic example and point to how to write a module for a more... realistic? larger? example?