Added directory structure outline and README files.

Added design choices documentation file for review.
 On branch master
 Changes to be committed:
   (use "git reset HEAD <file>..." to unstage)

	new file:   doc/README.md
	new file:   doc/design-choices.md
	new file:   src/rtl/README.md
   new file:   src/test/README.md
	new file:   tools/README.md