added README.md

Author: alfran

README.md

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+# Arduino Core for STM32F4 CPU
+
+This repository contains the source code and configuration files of the Arduino Core
+for ST Microelectronics STM32F4 processor (used on the Arduino STAR OTTO).
+
+## Installation on Arduino IDE
+
+This core is available as a package in the Arduino IDE cores manager.
+Just open the "Boards Manager" and install the package called:
+
+"Arduino STM32F4 Boards (32-bit ARM Cortex-M4)"
+
+## Support
+
+There is a dedicated section of the Arduino Forum for general discussion and project assistance:
+
+http://forum.arduino.org/index.php?board=98.0
+
+## Bugs or Issues
+
+If you find a bug you can submit an issue here on github:
+
+https://github.com/arduino/Arduino-core-stm32f4/issues
+
+Before posting a new issue, please check if the same problem has been already reported by someone else
+to avoid duplicates.
+
+## Contributions
+
+Contributions are always welcome. The preferred way to receive code cotribution is by submitting a
+Pull Request on github.
+
+## Hourly builds
+
+This repository is under a Continuous Integration system that every hour checks if there are updates and
+builds a release for testing (the so called "Hourly builds").
+
+The hourly builds are available through Boards Manager. If you want to install them:
+  1. Open the **Preferences** of the Arduino IDE.
+  2. Add this URL `http://downloads.arduino.cc/Hourly/STM32F4/package_stm32f4-hourly-build_index.json` in the **Additional Boards Manager URLs** field, and click OK.
+  3. Open the **Boards Manager** (menu Tools->Board->Board Manager...)
+  4. Install **Arduino STM32F4 core - Hourly build**
+  5. Select one of the boards under **STM32F4 Hourly build XX** in Tools->Board menu
+  6. Compile/Upload as usual
+
+If you already installed an hourly build and you want to update it with the latest:
+  1. Open the **Boards Manager** (menu Tools->Board->Board Manager...)
+  2. Remove **Arduino SAMD core - Hourly build**
+  3. Install again **Arduino SAMD core - Hourly build**, the Board Manager will download the latest build replacing the old one.
+
+## License and credits
+
+This core has been developed by Arduino.org in collaboration with STM.
+
+```
+  Copyright (c) 2017 Arduino.org  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  See the GNU Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA