Missing README

[josefdolezal]

As the app is getting closer to first release (🎉), we should add informations about project. Outline could be:

• [x] Motivation (just a short text about the app and why we made it)
• [x] tl; dr (quick guide how to setup environment)
• [x] TOC
• [x] Installation (brew, carthage (+ the --no-use-binaries trick for KeychainAccess), swiftgen)
• [x] Functions/Usage (list of implemented features, also gifs are nice)
• [x] Dependencies (list, licenses and links)
• [x] Help needed! (well, maybe somebody will be interested and help us with design or features implementation)
• [x] License

Maybe something come up later..

[josefdolezal]

Added in PR #27.