Updated README

Author: ondrejmirtes

README.md

@@ -19,6 +19,7 @@
 * Statically declared methods are called statically.
 * Disallow `empty()` - it's a very loose comparison (see [manual](https://php.net/empty)), it's recommended to use more strict one.
 * Always true `instanceof`, type-checking `is_*` functions and strict comparisons `===`/`!==`. These checks can be turned off by setting `checkAlwaysTrueInstanceof`/`checkAlwaysTrueCheckTypeFunctionCall`/`checkAlwaysTrueStrictComparison` to false.
+* Require parameter and return typehints for functions and methods (either native or phpDocs)
 * Correct case for referenced and called function names.
 * Correct case for inherited and implemented method names.