Defined the CONTRIBUTORS text for this package.

CONTRIBUTORS.txt

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+For the purpose of tracking copyright, this is the list of individuals and
+organizations who have contributed source code to this Swift package.
+
+For employees of an organization/company where the copyright of work done
+by employees of that company is held by the company itself, only the company
+needs to be listed here.
+
+## COPYRIGHT HOLDERS
+
+- Röck+Cöde VoF. (all contributors with '@rock-n-code.com')
+
+## PROJECT AUTHORS
+
+- Javier Cicchelli <javier@rock-n-code.com>