[Raindrops]: Added Instruction Append for divmod(), math.fmod(), math.remainder(), % & operator.modulo (#3611)

* Added refences for divmod, fmod, remainder, modulo and operator.modulo

* Added comma on line 6 for clarity.

exercises/practice/raindrops/.docs/instructions.append.md

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+# Instructions append
+
+## How this Exercise is Structured in Python
+
+This exercise is best solved with Python's `%` ([modulo][modulo]) operator, which returns the remainder of positive integer division.
+It has a method equivalent, `operator.mod()` in the [operator module][operator-mod].
+
+
+Python also offers additional 'remainder' methods in the [math module][math-module].
+[`math.fmod()`][fmod] behaves like `%`, but operates on floats.
+[`math.remainder()`][remainder] implements a "step closest to zero" algorithm for the remainder of division.
+While we encourage you to get familiar with these methods, neither of these will exactly match the result of `%`, and are not recommended for use with this exercise.
+
+The built-in function [`divmod()`][divmod] will also give a remainder than matches `%` if used with two positive integers, but returns a `tuple` that needs to be unpacked.
+
+[divmod]: https://docs.python.org/3/library/functions.html#divmod
+[fmod]: https://docs.python.org/3/library/math.html#math.fmod
+[math-module]: https://docs.python.org/3/library/math.html
+[modulo]: https://www.programiz.com/python-programming/operators#arithmetic
+[operator-mod]: https://docs.python.org/3/library/operator.html#operator.mod
+[remainder]: https://docs.python.org/3/library/math.html#math.remainder