[io grant] Add "The Basics" section to TDIOG

(Links to currently non-existent IO::CatHandle, but it will
exist soon)

Author: zoffixznet

doc/Language/io-guide.pod6

@@ -4,6 +4,31 @@
 
 =SUBTITLE Correctly use Perl 6 IO
 
+=head1 The Basics
+
+The vast majority of common IO work is done by the L<IO::Path> type. If you
+want to read from or write to a file in some form or shape, this is the class
+you want. It abstracts away the details of file handles (or "file descriptors")
+and so you mostly don't even have to think about them.
+
+Behind the scenes, L<IO::Path> works with L<IO::Handle>; a class which you
+can use directly if you need a bit more control than what L<IO::Path>
+provides. When working with other processes, e.g. via L<Proc> or L<Proc::Async>
+types, you'll also be dealing with a I<subclass> of L<IO::Handle>: the
+L<IO::Pipe>.
+
+Lastly, you have the L<IO::CatHandle>, as well as L<IO::Spec> and its
+subclasses, that you'll rarely, if ever, use directly. These classes give you
+advanced features, such as operating on multiple files as one handle, or
+low-level path manipulations.
+
+Along with all these classes, Perl 6 provides several subroutines that provide
+let you indirectly work with these classes. These come in handy if you like
+functional programming style or in Perl 6 one liners.
+
+While L<IO::Socket> and its subclasses also have to do with Input and Output,
+this guide does not cover them.
+
 =head1 The Wrong Way To Do Things
 
 This section describes how NOT to do Perl 6 IO.