update docs for new compiler default change (#513)

* update docs for new compiler whatever greg you know what i mean

Author: kshea21

tutorial_basics.rst

@@ -373,9 +373,7 @@ Spack can also use compilers built by Spack to compile later packages.
 .. literalinclude:: outputs/basics/compilers-2.out
    :language: spec
 
-Because this compiler is a newer version than the external compilers Spack knows about, it will be the new default compiler.
-We will discuss changing these defaults in a later section.
-We can check that this compiler is preferred by looking at the install plan for a package that isn't being reused from binary.
+Now ``gcc@12`` is immediately available to use.
 
 .. literalinclude:: outputs/basics/spec-zziplib.out
    :language: spec