update(readme): nicely organize topics

add(collections): pigify exercise

add(collections): exercises solution link

update(strings): improved the docs

update(hello-cargo): wording, and cargo book link

add: readme.md link to the collection exercises

Merge pull request #1 from jermyn626/fix-ownership-move

fix(ownership/move): correct "treat" to "trait"

update: collection exercises 1

update: slices tutorial

add: mode exercise solution

fix: collections exercises path

add: exercises link to README

add: exercises for collections

add: faq to resources