Migrate documentation

[akirak]

Due to the rewrite #5, configuration and usage sections in the README are deprecated. I also plan to migrate most of the documentation to the wiki, because I want to include a considerable amount of supplementary information and frequent commits on documentation can be noisy in the commit history.

The following is a list of subtasks:

• [x] Move references to other packages to "Inspirations" page
• [x] Add "Design" page which documents technical aspects of the package
• [x] Update the design goals on the current rewrite of the package
• [ ] (Optional) roadmap?

Eventually, design details will be added to Design page. The section should describe how frame-workflow actually works in detail.

[akirak]

Basic configuration and usage remain in README.