Update README.md

Addition to the readme, we linked the webpage were we deploy the documentation at the moment

README.md

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 **A**ngular momentum of
 **N**anostructures
 
+TITAN has been further developed under a closed repo, but we plan to release it in the near future. Temporary documentation can be found [here](https://titan.iffgit.fz-juelich.de/TITAN/)
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 A paper containing a detailed description of the method used in the code is in preparation. In the meantime, we shall greatly appreciate if scientific work done using **TITAN** will contain an explicit acknowledgement and the following reference:<br>
 F. S. M. Guimarães et al., Sci. Rep. 7, 3686 (2017)<br>
 https://www.nature.com/articles/s41598-017-03924-1