Update README.md with the rules and card effect mapping.

Resolves #1.

README.md

@@ -1,11 +1,58 @@
 # Short Circuit, created at #DroidconHack15
+
+A NFC enabled card game about battery drain. 1 to 4 players.
+
 Created by [Andrew Jack](https://twitter.com/andr3wjack), [Sam Parkinson](https://twitter.com/samparkinson_), [Laith Nurie](https://twitter.com/laith_nurie), [Ted Eriksson](https://twitter.com/Ted_Eriksson)
 
+
 ## Setting up Google Play Services Nearby
 Follow [this](https://developers.google.com/nearby/messages/android/get-started) guide to obtain a API key for the nearby API. Once obtained add it to the manifest file.
 
 I recommend replacing 'keys/shortcircuit.keystore' with a new one before obtaining an API key for it.
 
+## Rules
+
+### Setup
+
+* Shuffle the deck and place it face down within reach of all players
+* Each player should be dealt one card
+* The player with the lowest battery goes first
+
+### Gameplay
+
+* Draw a card from the top of the deck
+* Play a card from your hand, then add it to a discard pile
+* When there are no more cards, or there is only 1 player left with a charge the round ends
+
+The winner is the player with the most charge remaining.
+
+Tap cards on the battery that should be affected.
+
+## Card Mappings
+
+Card ID | Card Effect
+--------|------------
+1 | Charge 10%
+2 | Charge 10%
+3 | Charge 20%
+4 | Charge 30%
+5 | Drain 10%
+6 | Drain 10% * 2
+7 | Drain 20%
+8 | Drain 30% * 2
+9 | Drain 40%
+10 | Drain 50%
+11 | Drain half your current charge!
+12 | Steal 10% charge from another player
+13 | Steal 20% charge from another player
+14 | Steal 10% charge from every other player
+15 | Select another player to drain 20% charge
+16 | Select another player to drain 20% charge
+17 | Select another player to gain 10% charge
+18 | Select another player to drain 30% charge
+19 | Select another player to drain 30% charge
+20 | Every player drains 20%!
+
 License
 -------