Write a README

[PawelLipski]

• CI + License + Maven badge (shields.io, see https://github.com/VirtusLab/git-machete-intellij-plugin/ for a sample)
• Logo (Request a logo from the graphics team #25)
• Build setup (compiler plugin + dependency)
• Rationale: why Jackson sucks for Akka and how it's done better here
• Remember about explicit mentions of Borer! so that it doesn't create an impression that we attribute to ourselves what's actually done by Borer
• Document sbt settings for dump event schema plugin/options for compiler plugin (maybe not in README but in a separate file? TBD)
• Document Circe serializer with some Scala snippets

[MarconZet]

3, 4 and 5 done by #39