docs(string_tokenizer_count): add description for exercise

subjects/devops/string_tokenizer_count/README.md

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+## string_tokenizer_count
+
+### Instructions
+
+Create a file string_tokenizer_count.py that contains a function tokenizer_counter which takes in a string as a parameter and returns a dictionary of words and their count in the string.
+
+- The function should remove any punctuation from the string and convert it to lowercase before counting the words.
+
+- The function should return a dictionary of words and their count, sorted alphabetically by word.
+
+### Usage
+
+Here is an example of how to use the function:
+
+```python
+string = "This is a test sentence, with various words and 123 numbers!"
+result = tokenizer_counter(string)
+print(string)
+```
+
+And its output:
+
+```console
+string = "This is a test sentence, with various words and 123 numbers!"
+result = tokenizer_counter(string)
+```
+
+### Hints
+
+- The `re` module can be used to remove non-alphanumeric characters.
+
+- The `collections` module can be used to count the words.
+
+- The `operator` module can be used to sort the dictionary alphabetically by word.
+
+### References
+
+- [`re` module](https://docs.python.org/3/library/re.html)
+
+- [`collections` module](https://docs.python.org/3/library/collections.html)
+
+- [`operator` module](https://docs.python.org/3/library/operator.html)