Update README.md

Link to tutorial was broken

Author: edsaac

README.md

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 trame - a web framework that weaves together open source components into customized visual analytics easily.
 
 Please use the links below to find more informations:
-- [Tutorial](https://kitware.github.io/trame/docs/tutorial.html)
+- [Tutorial](https://kitware.github.io/trame/guide/tutorial/)
 - [trame website](https://kitware.github.io/trame/)