Adds information on Installation
Adds information on Installation

And, along with it, some other `CompUnit` classes in the same source file. This would do with yet another 3-figures issues, closes #502

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