Move the note about $*IN and friends in their section.
Move the note about $*IN and friends in their section.

Partially related to issue #1955

perl6/doc,tbrowder/doc,stmuk/doc,jonathanstowe/doc,tbrowder/doc,MasterDuke17/doc,stmuk/doc,dmaestro/doc,dmaestro/doc,tbrowder/doc,MasterDuke17/doc,jonathanstowe/doc,dmaestro/doc,stmuk/doc,MasterDuke17/doc,jonathanstowe/doc,jonathanstowe/doc,perl6/doc,stmuk/doc,perl6/doc,jonathanstowe/doc,stmuk/doc,tbrowder/doc,dmaestro/doc,dmaestro/doc,MasterDuke17/doc,perl6/doc,perl6/doc