[docs] Add a build doc

.gitignore

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-output
-build/device/elf2dfu.pyc
+/output/
 build/device/**/*.pyc

docs/build/index.md

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+---
+title: Installing the SDK — Software Engineering
+layout: breadcrumb
+breadcrumb: SDK
+---
+# Build and run your own version of Epsilon
+
+## Install the SDK
+
+### Windows
+
+We recommend using the [Msys2](https://www.msys2.org/) environment to install all the required tools. We support Windows 7 and up. Once Msys2 has been installed, launch the Msys2 terminal application, and enter the following commands
+
+```
+pacman -S mingw-w64-x86_64-gcc mingw-w64-x86_64-freetype mingw-w64-x86_64-pkg-config mingw-w64-x86_64-fltk git make bison python
+export PATH=/mingw64/bin:$PATH
+```
+
+### macOS
+
+We recommend using [Homebrew](https://brew.sh) to install most dependencies. Once you have installed Homebrew, install all the dependencies with the following command:
+
+```
+brew reinstall fltk freetype dfu-util libpng pkg-config
+brew cask reinstall gcc-arm-embedded
+```
+
+### Debian or Ubuntu
+
+Installing the required tools is just a command away:
+
+```
+apt-get install bison build-essential dfu-util flex gcc-arm-none-eabi git libfltk1.3-dev libfreetype6-dev libpng12-dev
+```
+
+## Retrieve the source code
+
+The code is hosted on <a href="https://github.com/numworks/epsilon">GitHub</a>. You can retrieve it using the follwing command.
+
+```
+git clone https://github.com/numworks/epsilon.git
+```
+
+## Run Epsilon on your computer
+
+Once the SDK has been installed, just open your terminal (Msys2, Terminal.app, xterm, etc...) and type the following commands:
+
+```
+make PLATFORM=simulator clean
+make PLATFORM=simulator
+./epsilon.elf
+```
+
+## Run Epsilon on your calculator
+
+You can also update your NumWorks calculator easily. Note that you'll need to press the Reset button and that all data on your calculator will be lost.
+
+```
+make clean
+make
+make epsilon_flash
+```
+
+## What's next
+Congratulations, you've built your first firmware! If you want to dive deeper into the code, you can either read about our <a href="../embedded/">design considerations</a> or discover <a href="../architecture/">Epsilon's architecture</a>.