docs: readme for radix sort

Author: yeoshuheng

src/main/java/algorithms/sorting/radixSort/README.md

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+# Radix Sort
+
+Radix Sort is a non-comparison based, stable sorting algorithm. 
+We first treat each element as a string with *w* digits (Padding elements that have 
+less than *w* digits).
+
+From the least-significant digit to the most-significant digit, we constantly 
+split them into ten queues corresponding to the number range *[0, 9]*. We then move 
+through the queue and concatenate the elements back into a list at the next iteration.
+
+This takes advantage of the concept of place value. 
+(The value of a digit in a number relative to its position within the number)
+
+![Radix Sort](https://miro.medium.com/v2/resize:fit:661/1*xFnpQ4UNK0TvyxiL8r1svg.png)
+
+*Source: Level Up Coding* 
+
+## Complexity Analysis
+**Time**:
+Note that we will always need to iterate through 10 different queues to rebuild our original array,
+and we iterate through all *w* positions, this results in:
+
+- Worst case: O(w * (n + 10))
+- Average case: O(w * (n + 10))
+- Best case (sorted array): O(w * (n + 10))
+
+**Space**: O(n + k) 
+
+## Notes
+- Radix sort's time complexity is dependent on the maximum number of digits in each element,
+hence it is ideal to use it on integers with a large range and with little digits.
+- This could mean that Radix Sort might end up performing worst on small sets of data 
+if any one given element has a in-proportionate amount of digits.
+- Counting sort is used as a sub-routine within the Radix Sort process.
+
+### Common Misconception
+- While not immediately obvious, we can see that radix sort is a stable sorting algorithm as
+  they are enqueued in a manner where the first observed element will be at the head of the queue.
+- While it is non-comparison based, not that total ordering of elements is still required -
+  except now this property is forced upon the algorithm in the manner of the queues.