Updated Developer's Guide (markdown)

Developer's-Guide.md

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-WIP
+Welcome to the dev guide !
+
+## Technical sum up
+
+DCS Liberation is coded in Python, with QT5 as UI framework.
+It uses pyDCS to generate DCS World missions.
+
+Before contributing to DCS Liberation, you should also maybe consider contributing to [PyDCS](https://github.com/pydcs/dcs), this is a great way to contribute indirectly to the project.
+
+## Project history
+
+DCS Liberation was a project started in 2018 by shdwp, original repo is still available here : https://github.com/shdwp/dcs_liberation
+The original UI was different, and the mission generation process was different as well from version 2.0+
+
+## Required tools
+
+* [Python 3.6+](https://www.python.org/downloads/)
+* A code Editor for Python. I recommend [PyCharm Community Edition](https://www.jetbrains.com/pycharm/download/#section=windows), you can add plugin for Lua.
+
+When you install Python, make sure to install pip for dependencies management.
+
+## Checkout the repository code with git
+
+**master branch** : Should be even with current release version
+**develop branch** : Current version being worked on, might be unstable
+
+## Installing dependencies
+
+pip install -r requirements.txt
+
+## Running from sources
+