update prefer-while docs

Author: ajafff

docs/prefer-while.md

@@ -2,6 +2,8 @@
 
 A `for`-loop without initializer and incrementer can also be rewritten as `while`-loop. This rule can automatically fix errors.
 
+:warning: As of TSLint v5.10.0 this rule is a TSLint core rule. You will no longer be able to use the rule from this package.
+
 ```ts
 for (;;)
     doStuff();