Added License, Contributibng guide and GPLv3 header

CONTRIBUTING.md

@@ -1 +1,14 @@
-Foo bar
+# How to contribute
+
+This project is open source and licensed under the GPLv3. If you want to contribute code, you must first agree to our [CLA (Contributor License Agreement)](./licenses/cla.md) .
+By doing so, you give us the possibility to develop Robotmk and its tools tailor-made for Checkmk; parts of Robotmk will be available under the name "Synthetic Monitoring for Checkmk" as an enterprise product for Checkmk. Your agreement to the CLA allows us to use program lines contributed by you in the Enterprise part.
+
+# What are the consequences of agreeing to the cla?
+
+By agreeing to the CLa, you are no longer the sole owner of the copyright to the code you contributed. Among other things, you give up the right to take legal action against us for allowing tribe29 to use Robotmk under a license other than GPLv3.
+This formal and bureaucratic act is unfortunately necessary - but we want to communicate this as openly as possible. In the end, everything serves the goal of making Robotmk even better.
+
+## Ok, how can I agree to the CLA?
+
+After you submit a pull request, you will see that it is commented by the "CLA Assistant" bot. It will ask you to comment the pull request with the text "I have read the CLA Document and I hereby sign the CLA".
+Once this comment is recognized, the bot will add you to the list of contributors. Your pull request can then be reviewed and accepted.

CheckmkLibrary/checkmklibrary.py

@@ -1,3 +1,6 @@
+# SPDX-FileCopyrightText: © 2022 ELABIT GmbH <[email protected]>
+# SPDX-License-Identifier: GPL-3.0-or-later
+
 from robot.api import logger
 from robot.api.exceptions import Failure, Error
 from robot.api.deco import library, keyword