open a file by its name without having to provide a fully qualified path.
Configure the 'path'
'path' option allows us to specify a set of directories inside of which Vim will search when
:findcommand is invoked.
**: matches all subdirectories beneath the app/ directory.
Use :find to Look up Files by Name
after first Tab, vim expands the entire path of the first full match. after second Tab, vim expands the next matching full filepath.