updates doc

doc/USER_MANUAL/02_getting_started.tex

@@ -505,6 +505,9 @@ \section{Visualizing the subroutine calling tree of the source code}
 \section{Becoming a developer of the code, or making small modifications in the source code}
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-If you want to develop new features in the code, and/or if you want to make small changes, improvements, or bug fixes, you are very welcome to contribute. To do so, i.e. to access the development branch of the source code with read/write access (in a safe way, no need to worry too much about breaking the package, there are CI tests based on BuildBot, Travis-CI and Jenkins in place that are checking and validating all new contributions and changes), please visit this Web page:\newline
+If you want to develop new features in the code, and/or if you want to make small changes, improvements, or bug fixes, you are very welcome to contribute!
+To do so, i.e. to access the development branch of the source code with read/write access (in a safe way, no need to worry too much about breaking the package,
+there are CI tests based on BuildBot, Travis-CI and Jenkins in place that are checking and validating all new contributions and changes),
+please visit this Web page:\newline
 \url{https://github.com/SPECFEM/specfem3d/wiki}