docs clean up and additions for build_targets

Did some "clean up" (my opinion only) to remove line wrap over 80 chars where possible. Added docs for build_targets which is located https://github.com/maxamillion/tito/pull/new/dgoodwin:master...maxamillion:docs#L0R76

If in the event the "clean up" is preferred to be removed and leave the line wrapping in there I will happily modify this commit to only include the build_targets addition.