Merge pull request #177 from control-toolbox/readme

Update README.md

README.md

@@ -18,7 +18,8 @@
 [release-img]: https://img.shields.io/github/v/release/control-toolbox/CTBase.jl.svg?style=round-square
 [release-url]: https://github.com/control-toolbox/CTBase.jl/releases
 
-The `CTBase.jl` package is part of the [control-toolbox ecosystem](https://github.com/control-toolbox).
+The `CTBase.jl` package is part of the [control-toolbox ecosystem](https://github.com/control-toolbox). 
+The control-toolbox ecosystem gathers `Julia` packages for mathematical control and applications. The root package is [`OptimalControl.jl`](https://github.com/control-toolbox/OptimalControl.jl) which aims to provide tools to modelise and solve optimal control problems by direct and indirect methods. [![doc OptimalControl.jl](https://img.shields.io/badge/doc-OptimalControl.jl-blue)](http://control-toolbox.org/docs/optimalcontrol)
 
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