[Documentation] Please add two entries to https://crystal-lang.org/reference/1.5/using_the_compiler/index.html - one for compiling multiple .cr files, and one for integrating shards

[rubyFeedback]

I finally started to learn crystal and have progressed to noob level 2, mostly.

I can compile my crystal code fine. \o/

However had right now I am compiling only single .cr files.

Could the official documentation add a paragraph that deals with
multiple .cr files? Do we have to specify them on the commandline?
What if these resides in other directories?

And, second to that, how to integrate code stored in shards, when we
want to compile something. Will the shards become a part of the resulting
binary?

This is probably easy to know for you guys, but as a newcomer it is not
yet clear to me, which is why i propose to add it to the official tutorial.
(I don't really want to check other resources, but admittedly I actually
learned the most so far from other blog entries that explain stuff.
Examples on the official homepage work fine though, I learn fastest
with working examples via the commandline actually.)

[Blacksmoke16]

This should prob be moved to https://github.com/crystal-lang/crystal-book.

But to answer your question, you should checkout https://crystal-lang.org/reference/1.5/syntax_and_semantics/requiring_files.html which covers essentially how to do both of these things.