add annotations for thrown exceptions

src/Generator/CombGenerator.php

@@ -53,6 +53,9 @@ class CombGenerator implements RandomGeneratorInterface
      *
      * @param integer $length The number of bytes of random binary data to generate
      * @return string A binary string
+     * @throws \Ramsey\Uuid\Exception\UnsatisfiedDependencyException if `Moontoast\Math\BigNumber` is not present
+     * @throws \InvalidArgumentException if length is not a positive integer
+     * @throws \Exception
      */
     public function generate($length)
     {