Add readme file.

README.md

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+Termux Proxmark3 Client
+=======================
+
+This script helps you to compile and run the [Proxmark3](http://www.proxmark.org/) client on Android. No special
+software is needed, just the [Termux](https://termux.com/) app.
+
+The script will install the [RDV4 version](https://github.com/RfidResearchGroup/proxmark3) of the client.
+
+
+
+Requirements
+------------
+
+* Android device with root access and USB-OTG support
+* USB-OTG adapter
+* [Termux app](https://termux.com/)
+* Proxmark3 with the latest (git master branch) [RDV4 firmware](https://github.com/RfidResearchGroup/proxmark3)
+flashed on it
+
+Root access is needed for now. There are plans in the Termux community to support USB-OTG and Bluetooth devices.
+It should be possible to drop the root requirement once Termux has USB-OTG and/or Bluetooth support.
+
+
+
+Installation
+------------
+
+Run the following commands in Termux:
+```
+pkg install git
+git clone https://github.com/ikarus23/termux-pm3.git
+cd termux-pm3
+bash termux-pm3.sh install
+```
+There are some issues with Android 5.x and 7.x (and maybe other) which stops the compiling process.
+Try the following command, it might help:
+```
+bash termux-pm3-sh install ignore-warnings
+```
+If you don't have a Proxmark RDV4 you need to add the `PLATFORM=PM3OTHER` flag. You might also want to check out
+`PLATFORM=help`.
+```
+bash termux-pm3-sh install [ignore-warnings] PLATFORM=PM3OTHER
+```
+Another hint: Do not run this script from within `/sdcard`. This could lead to troubles regarding the
+permission to execute a binary. Just run it from within the Termux root (default) directory.
+
+
+
+Usage
+-----
+
+Connect the Proxmark3 via USB-OTG to your Android device and run the following command from within the
+`termux-pm3` folder in Termux:
+```
+bash termux-pm3.sh run
+```
+To update the Proxmark3 client just run:
+```
+bash termux-pm3.sh update [ignore-warnings] [PLATFORM=PM3OTHER]
+```