Add reference and a quick intro for the arabic stemmer in snowball website

[assem-ch]

http://snowballstem.org/algorithms/

[ojwb]

Hi Assem, hope you're well.

I've just added a page to the snowball website for Arabic but it only has the automatically generated stuff currently and information that was already present elsewhere:

https://snowballstem.org/algorithms/arabic/stemmer.html

It'd be good to have some reference material here - especially recording design decisions made in cases where there are tradeoffs and the reasons for making those choices.

One quick and fairly easy improvement would be to enable the example stemmer output - this is generated by a function call in the template algorithms/arabic/stemmer.tt in the snowball-website repo:

[% #algorithm_vocab([12, 'example', 'test']) %]

Removing the # will enable it, but it needs two suitable Arabic words in place of example and test, and a count for how many words to show stems for starting from each of those two words (in place of 12). We want to pick words (and a number) that show the stemming working well, which is hard for me to do as I can't read Arabic.

You can see the English sample stems here:

https://snowballstem.org/algorithms/english/stemmer.html

[assem-ch]

I will write it or guide someone to do it, thank you for reportimg