Add reviewer checklist to the guides

Author: chahank

Reviewer_Checklist.md

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+# Reviewer Checklist
+
+* Include references to the used algorithms in the docstring
+* If the algorithm is new, please include a description in the docstring, or be sure to include a reference as soon as you publish the work
+* The code should be easily readable (for infos e.g. here [here](https://treyhunner.com/2017/07/craft-your-python-like-poetry/?__s=jf8h91lx6zhl7vv6o9jo))
+* Variable names should be chosen to be clear. Avoid `item, element, var, list` etc... 
+* Avoid as much as possible hard-coded indices for list (no `x = l[0], y = l[1]`) (see also [here](https://treyhunner.com/2018/03/tuple-unpacking-improves-python-code-readability/))
+* Use pythonic loops, list comprehensions etc.
+* Make sure the unit test are testing all the relevant parts of the code
+* Check the docstring (is everything clearly explained, are the default values given an clear)