📚 Add AUTHORS.md file

AUTHORS.md

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+SatelliteToolbox.jl
+===================
+
+**INPE - Brazilian National Institute for Space Research**  
+**CGETE - Department of Space Engineering and Technology**  
+**DIDSE - Space Systems Division**
+
+The initial versions of **SatelliteToolbox.jl** were developed by Dr. Ronan
+Arraes Jardim Chagas at the [Brazilian National Institute for Space
+Research](http://www.inpe.br) (INPE). The toolbox was released to the general
+public at **May 13, 2018**.
+
+The list of contributors can be seen
+[here](https://github.com/JuliaSpace/SatelliteToolbox.jl/graphs/contributors).