master 5308a4e11e: Improve image-tests.el Commentary

[Eli Zaretskii <eliz@gnu.org>]

> --- a/test/src/image-tests.el
> +++ b/test/src/image-tests.el
> @@ -22,8 +22,11 @@
>  ;;; Commentary:
>  
>  ;; Most of these tests will only run in a GUI session, and not with
> -;; "make check".  Run them manually in an interactive session with
> -;; `M-x eval-buffer' followed by `M-x ert'.
> +;; "make check".  You must run them manually in an interactive session
> +;; with, for example, `M-x eval-buffer' followed by `M-x ert'.
> +;;
> +;; To run these tests from the command line, try:
> +;;     ./src/emacs -Q -l test/src/image-tests.el -eval "(ert t)"

IMO, the above means that these tests should be moved out of test/src,
and into test/manual/.  That's where we put all the tests that must be
run manually.

Thanks.