[articles/typography/justification] Add some pictures

[r12a]

[source] (http://w3c.github.io/i18n-drafts/articles/typography/justification.en.html) [en]

It would be nice to have pictures for each of the writing systems mentioned that show a nicely justified piece of text that exhibits one or two of the features described.

For example, https://w3c.github.io/elreq/#spacing_threshold_following_full_stop shows Ethiopic text.

[r12a]

here's a good example for Japanese
https://www.w3.org/TR/jlreq/Images-en/img2_33.png

and here's one for Tibetan
http://w3c.github.io/tlreq/images/tsek-justification.jpg

it would be nice to also have one for Arabic, but i don't think we need more.

[r12a]

Done.