Update README.md

Merge branch 'develop'

Merge branch 'fix-not_showing_books' into develop

edit: upgraded versions

added: constructor annotation for simple xml deserialization

added: proguard rules to keep the entities intact after obfuscation.

edit: search response test.

deleted: google-services.json

edit: added google services to gitignore

edit: added google services to gitignore

edit: gitignore now ignores google-services.json

added: simple xml rules

edit: changed presenter type from SearchPresenter to SearchBooksContract.Presenter

Merge branch 'fix_signing_error' into develop

updated: git ignore.