Adjust readme, fix another PHP 8.1 issue in Cursor

Author: samdark

README.md

@@ -35,10 +35,10 @@ php composer.phar require --prefer-dist yiisoft/yii2-mongodb
 or add
 
 ```
-"yiisoft/yii2-mongodb": "~2.1.0"
+"yiisoft/yii2-mongodb": "~3.0.0"
 ```
 
-to the require section of your composer.json.
+to the `require` section of your `composer.json`.
 
 Configuration
 -------------

src/file/Cursor.php

@@ -55,6 +55,7 @@ public function current()
  * This method is required by the interface [[\Countable]].
  * @return int elements count.
  */
+ #[\ReturnTypeWillChange]
  public function count()
  {
  return count($this->cursor);