Add CHANGELOG

CHANGELOG

+# Changelog
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [0.0.1] - 2019-02-22
+## First beta release version
+### Added (list of core functionality)
+- you can track your menstrual bleeding
+- you can track symptoms related to natural family planning (nfp), i.e. basal temperature and mucus or cervix
+- you can use nfp symptoms for fertility awareness (drip implements the sympto-thermal method)
+- you can track other symptoms like desire, sex, pain, mood, or save a note
+- you can see bleeding days and predicted bleeding days in a calendar
+- drip gives you an overview of tracked symptoms on a beautiful chart
+- you can see basic stats about your cycle lengths
+- you can encrypt your data and protect it with a password
+- you can import and export your data in a nice format (csv)
+- you can set reminders (daily reminder for taking your temperature or once per cycle for your next period
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