Fix typos on zef option.
Fix typos on zef option.

Remove extra explaination about 'node' executable.
See discussion at <https://github.com/perl6/doc/pull/1700>.

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