Add links and correct locations in project/README.md

After removing the duplicate ROADMAP in a separate PR, a few other
issues were noted in README.md which are fixed here:
- the directory is project, not hack
- make.sh is no longer in the current dir since hack/ is not project/
  anymore
- MAINTAINERS is no longer here as a markdown file, but is a TOML file
  in the root of the project
- links were added to all files to make it easier to follow from here
  to the appropriate location

Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)