Improve link installation

1. Make it agnostic of the git checkout directory by using CURDIR.
2. Make it create the links forcefully so that moving the directoy
   and running make install will see links updated.

Signed-off-by: Ben Walton <bdwalton@gmail.com>
have the default make target print a small help message instead of immediately installing links

Signed-off-by: Ben Walton <bdwalton@gmail.com>