Update app description and add F-Droid badge in README.

Author: philliphsu

README.md

@@ -1,13 +1,27 @@
 # Clock+
-Clock+ is an alternative to the Google Clock app for Android, featuring UI/UX enhancements and new time pickers.
+Clock+ is a simple alarm clock, timer, and stopwatch app that offers a delightful user experience
+for all your timing needs.
 
-<a href='https://play.google.com/store/apps/details?id=com.philliphsu.clock2&utm_source=global_co&utm_medium=prtnr&utm_content=Mar2515&utm_campaign=PartBadge&pcampaignid=MKT-Other-global-all-co-prtnr-py-PartBadge-Mar2515-1'><img alt='Get it on Google Play' src='https://play.google.com/intl/en_us/badges/images/generic/en_badge_web_generic.png'/></a>
+Highlights:
+
+- **Clean, minimalistic design:** Features Material Design throughout.
+- **New time pickers:** Enjoy setting alarms with two new time pickers! Beautifully crafted and
+intuitively designed for ease of use.
+- **List of timers:** See all of your timers in one scrollable list, and control each one individually.
+- **Themes:** Choose between light, dark, and black themes.
+
+[<img src="https://play.google.com/intl/en_us/badges/images/generic/en_badge_web_generic.png"
+      alt="Get it on Google Play"
+      height="80">](https://play.google.com/store/apps/details?id=com.philliphsu.clock2)
+[<img src="https://f-droid.org/badge/get-it-on.png"
+      alt="Get it on F-Droid"
+      height="80">](https://f-droid.org/app/com.philliphsu.clock2)
 
 <img src="https://cloud.githubusercontent.com/assets/19766085/19008497/830d2844-8720-11e6-8b8e-ff01ebcc26fe.png" width="180" height="320" />
 <img src="https://cloud.githubusercontent.com/assets/19766085/19008498/8312eeaa-8720-11e6-9dc8-2079eb9c50f7.png" width="180" height="320" />
 <img src="https://cloud.githubusercontent.com/assets/19766085/19008382/cc800614-871f-11e6-8fab-d1be69807e91.png" height="320" />
 
-# License
+## License
 ```
 Copyright 2017 Phillip Hsu