make `add` feature add all files in the root of the git directory from pwd

[AleixMT]

Basically, instead of having add as alias for git add, we can include the behaviour of adding all files of the git project that the pwd is in. so basically if I am in a directory like this:

/my/git/project/subfolder1/subfolder2

add should add all files as in git add /my/git/project