prefer-default-parameters - Document falsy values (#2423)

Author: fregante

docs/rules/prefer-default-parameters.md

@@ -9,6 +9,8 @@
 
 Instead of reassigning a function parameter, default parameters should be used. The `foo = foo || 123` statement evaluates to `123` when `foo` is falsy, possibly leading to confusing behavior, whereas default parameters only apply when passed an `undefined` value. This rule only reports reassignments to literal values.
 
+You should disable this rule if you want your functions to deal with `null` and other falsy values the same way as `undefined`. Default parameters are exclusively applied [when `undefined` is received.](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters#passing_undefined_vs._other_falsy_values). However, we recommend [moving away from `null`](https://github.com/sindresorhus/meta/discussions/7).
+
 ## Fail
 
 ```js