improve doc comments

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

syft/source/location.go

@@ -7,18 +7,21 @@ import (
 	"github.com/anchore/stereoscope/pkg/image"
 )
 
+// Location represents a path relative to a particular filesystem.
 type Location struct {
-	Path         string `json:"path"`
-	FileSystemID string `json:"layerID,omitempty"` // TODO: comment
-	ref          file.Reference
+	Path         string         `json:"path"`              // The string path of the location (e.g. /etc/hosts)
+	FileSystemID string         `json:"layerID,omitempty"` // An ID representing the filesystem. For container images this is a layer digest, directories or root filesystem this is blank.
+	ref          file.Reference // The file reference relative to the stereoscope.FileCatalog that has more information about this location.
 }
 
+// NewLocation creates a new Location representing a path without denoting a filesystem or FileCatalog reference.
 func NewLocation(path string) Location {
 	return Location{
 		Path: path,
 	}
 }
 
+// NewLocationFromImage creates a new Location representing the given path (extracted from the ref) relative to the given image.
 func NewLocationFromImage(ref file.Reference, img *image.Image) Location {
 	entry, err := img.FileCatalog.Get(ref)
 	if err != nil {