Improve docs to avoid Risky test warnings

Author: aik099

README.md

@@ -67,6 +67,14 @@ assertThat($result === true);
 assertThat(true, is(true));
 ```
 
+:warning: To prevent tests from being marked as Risky (the `This test did not perform any assertions` message)
+add this code to your test case `tearDown` method:
+
+```php
+$this->addToAssertionCount(\Hamcrest\MatcherAssert::getCount());
+\Hamcrest\MatcherAssert::resetCount();
+```
+
 :warning: **NOTE:** the global proxy-functions aren't autoloaded by default, so you will need to load them first:
 
 ```php