add the design.md for the calculator-conundrum

Author: xinri

exercises/concept/calculator-conundrum/.meta/design.md

@@ -18,3 +18,16 @@
 
 - `conditionals-if`: know how to do conditional logic.
 - `switch-statement`: know how to work with a `switch` statement.
+
+## Analyzer
+
+This exercise could benefit from the following rules in the [analyzer]:
+
+- `essential`: Verify that the solution is not wrapping all the code in a try catch statement
+- `actionable`: If the solution uses an `if` statement, instruct the student to use the `switch case` statement instead.
+- `informative`: If the solution does not use `HashMap`, instruct the student to use the operator as a key and a BiFunction implementing the calculation
+  Explain that it is more efficient for performance, and it removes the cyclomatic complexity
+- `informative`: If the solution does not throw the exception for `Operation cannot be null` and `Operation cannot be empty` at the beginning, instruct the student to do so
+  Explain that it is better to fail fast, and it will make the code less error-prone and more readable
+
+[analyzer]: https://github.com/exercism/java-analyzer