documentation: include effects

[odeke-em]

We launched a bunch of effects usable in our editor and the world uses them in our editor. However, we need to propagate this back to show developers how to use our API to achieve the same effects so that they can start building effects in their apps.

References:

• https://www.producthunt.com/tech/gifs-3.
• https://techcrunch.com/2016/05/05/gifs-com-launches-a-new-tool-to-augment-your-animated-gifs.