re-structure the package content

@BernhardKonrad I've started this branch to re-organize some things ...
default toc_depth is fine
add advice to run rstudio preview version
better instructions to prep system for package development
spaces
revising day one activity up through "The DESCRIPTION file"
Merge branch 'split-package-content' of https://github.com/STAT545-UBC/STAT545-UBC.github.io

Conflicts:
	packages02_activity.html
	packages02_activity.md