Add link to ANKIdroid

[truedat101]

This looks like a great little project for EDU: https://code.google.com/p/ankidroid/

We should (1) try it out (2) provide a link to the download (3) don't put the download on the server (4) add the download directly in the firmware BOM

[truedat101]

@chrqls can you install this software and evaluate its usefulness?

[truedat101]

Adding this: https://github.com/ankidroid/Anki-Android/issues

(it's moved).