Update documents of `dispatchAdd`
`ADD` does not support git.
Ref:
@@ -89,7 +89,7 @@ func dispatchLabel(d dispatchRequest, c *instructions.LabelCommand) error {
// ADD foo /path
//
-// Add the file 'foo' to '/path'. Tarball and Remote URL (git, http) handling
+// Add the file 'foo' to '/path'. Tarball and Remote URL (http, https) handling
// exist here. If you do not wish to have this automatic handling, use COPY.
//
func dispatchAdd(d dispatchRequest, c *instructions.AddCommand) error {
