doc: point directly to zuul.conf section

The launcher documentation about 'Starting Builds' evokes the
parameter-function in the zuul.conf documentation.  One had to goes down
a few pages until the 'Includes' subsection.  I have updated the
references to point directly to Includes, saving the reader sometime.

Also fixed a typo: paremeter -> parameter

Change-Id: I560f857b40a7cb989a71161f94e1fb0c8fd69293
Merge "doc: point directly to zuul.conf section"