ref CONTRIBUTING.md to the leapp landing page (#507)

* Refer to the new contribution guidelines

CONTRIBUTING.md

@@ -1,68 +1 @@
-# Contribution guidelines for writing actors
-
-These guidelines are an addition to the [Leapp project contribution guidelines](https://github.com/oamg/leapp-guidelines/blob/master/contributing-guidelines.rst).
-
-## Coding guidelines
-
-1. The code should follow these documents as much as feasible:
-   - the [Leapp project Python coding guidelines](https://github.com/oamg/leapp-guidelines/blob/master/python-coding-guidelines.md).
-   - the [Best practices for writing actors](https://leapp.readthedocs.io/en/latest/best-practices.html)
-1. All Python code must be Python 2.7+/3.6+ compatible.
-1. Use of Python language for the actor's logic is **preferred**, even though you can call a script in any language from the actor's Python skeleton.
-
-## Tests
-
-1. Actors must include [component or unit tests](https://github.com/oamg/leapp-repository/blob/master/docs/tests.md).
-1. Bug fix PRs must include [tests](https://github.com/oamg/leapp-repository/blob/master/docs/tests.md) covering the fixed issue.
-
-## Naming convention
-
-1. New folders and/or Python files must use lowercase without underscores.
-   - with the exception of test file names, which need to be named `test_*.py` or `*_test.py`
-1. Do not use _actor_ in the actor's name, neither _model/topic/tag/phase_ in the model/topic/tag/phase name, as these things are implicit.
-1. The actor's main file must be named `actor.py`.
-
-## Code style
-
-1. Follow [PEP 8 - Style Guide for Python Code](https://www.python.org/dev/peps/pep-0008/)
-   - with the exception of line length which can be up to 120 characters
-   - use of linters (PyLint, pep8, flake8) is encouraged
-1. String and docstring convention
-   - Follow [PEP 257 - Docstring Conventions](https://www.python.org/dev/peps/pep-0257)
-      - with the exception, that the summary line of a multi-line docstring shall be on a new line, not on the same line as the opening quotes.
-   - Description in the docstring of actors, models and/or phases must conform to their implementation. Description of an actor should include the expected behaviour and inputs/outputs, so that one is able to write [component tests](https://github.com/oamg/leapp-repository/blob/master/docs/tests.md#component-tests) for the actor without looking at the actor's code.
-   - <details>
-       <summary>Click for the example of how to write strings and docstrings</summary>
-
-        ```python
-        class MyActor(Actor):
-            """
-            Start with a single-line brief summary of the actor (under the triple quotes).
-
-            Leave a blank line below the summary and then describe the actor's behaviour
-            here in detail.
-            """
-            name = 'my_actor'
-
-            def process(self):
-                """This is a simple method."""
-                complicated_method(True)
-
-            def complicated_method(switch):
-                """
-                This is a summary line of a more complicated method.
-
-                Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc porta sed
-                urna venenatis faucibus. Phasellus at bibendum ligula, a posuere metus.
-
-                :param switch: Description of the parameter.
-                :type switch: Expected type of the parameter.
-                :return: Description of what the method returns
-                """
-                mutliline_string = (
-                    'I am a multiline string.\n'
-                    'This is my second line.'
-                )
-                return mutliline_string
-        ```
-      </details>
+See the [Contribution guidelines](https://leapp.readthedocs.io/en/latest/contributing.html)