Created Install Emulationstation on Gameshell (markdown)

Install-Emulationstation-on-Gameshell.md

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+I specify here that this is the basic version of Emulationstation. Not that of Retropie or Recalbox. 
+
+Feel free to visit the [official Emulationstation github page](https://github.com/Aloshi/EmulationStation/) for more informations
+
+# Building
+Log in SSH on your Gameshell and go to your home directory.
+
+`cd /home/cpi`
+
+You need to install a few packages : 
+
+`sudo apt-get install libsdl2-dev libboost-system-dev libboost-filesystem-dev libboost-date-time-dev libboost-locale-dev libfreeimage-dev libfreetype6-dev libeigen3-dev libcurl4-openssl-dev libasound2-dev libgl1-mesa-dev build-essential cmake fonts-droid`
+
+Clone the git project : 
+
+`git clone https://github.com/Aloshi/EmulationStation.git`
+
+**NOTE**: by default you are on the **master** branch. A branch named _video_ exists and add the video preview support.
+
+> You can switch on the video branch by (not tested yet)
+
+> `git checkout remotes/origin/video` 
+
+Then, generate and build the Makefile with CMake:
+
+`cd EmulationStation`
+
+`cmake .`
+
+`make`
+
+This will take a few time.
+
+Now install emulationstation to /usr/local/bin/emulationstation, which will let you just type 'emulationstation' to run it, do:
+
+`sudo make install`
+
+# Add EmulationStation to launcher
+## Create entry
+Go to **/home/cpi/launcher/Menu/GameShell** and create a _XX_Emulationstation.sh_ file. Where XX is the number you want depending on the position in the launcher.
+
+Just add `emulationstation` inside.
+
+## Add an icon
+Go to **/home/cpi/launcher/skin/default/Menu/GameShell** and add _Emulationstation.png_
+
+# Configuring
+## Create es_systems.cfg
+
+**NOTE**: A system must have at least one game present in its "path" directory, or ES will ignore it! If no valid systems are found, ES will report an error and quit!
+
+Go to ~/.emulationstation/ and create the file es_systems.cfg :
+
+![](https://i.imgur.com/s0y6esu.png)
+
+## Create gamelist.xml
+
+in ~/.emulationstation/ create a floder named **gamelists**.
+
+We're following our SNES example by creating a **snes** folder in **gamelists** and a _gamelist.xml_ file inside.
+
+in ~/.emulationstation/ create a floder named **downloaded_images** and a **snes** folder inside.
+
+Edit your _gamelist.xml_ :
+
+![](https://i.imgur.com/ySDheqw.png)
+
+# Installing a more descent theme
+
+The default theme is not adapted for small resolution. Until you have something really optimized for a resolution of 320x240, you can install the GBZ35 theme 
+
+Go to the theme folder
+
+`cd /etc/emulationstation/themes`
+
+To insall light theme :
+`git clone https://github.com/rxbrad/es-theme-gbz35.git`
+
+To insall dark theme :
+`git clone https://github.com/rxbrad/es-theme-gbz35-dark`