[DRAFT] Method: Text alternative for Image of text

Jeanne and all,

I wrote up the first draft of the candidate method "Text alternative for
Image of text" by using the new Method template.

[DRAFT] Method: Text alternative for Image of text
https://docs.google.com/document/d/1h5IiwbIvsWZr8N2qXNm9NQBR46gQWmfvWpDvtxHxR9o/edit?usp=sharing

As I suggested on this Tuesday call, Alt text subgroup is going to use the
7 different types of images which are introduced in WAI Tutorial.
https://www.w3.org/WAI/tutorials/images/

"Images of text" is one of the 7 types. Alt Text subgroup will write
different methods like "Text alternatives for ..." :
* Informative images
* Decorative images
* Functional images
* Images of text
* Complex images
* Groups of images
* Image maps

I'm not sure if I did it right. It would be highly appreciated if you could
check this draft document.  Any feedback and questions are welcome.

Thanks,
Makoto