Suggestion: add Keyframes Player information to readme

[insidegui]

I made this app for macOS which initially allowed for the playback of Keyframes animations as a tool for debugging and previewing the animations exported from After Effects without having to import them in an app.

Today I released version 1.2, and with this version I added an export option. The feature exports a Core Animation archive of the animation, which means it can be integrated in an app without the need to include the Keyframes framework.

I believe this is an useful tool for users of the Keyframes project and it would be beneficial to have some information about it on the project readme.