Add link to php serialization

Author: jsoizo

formats/README.md

@@ -37,4 +37,5 @@ For convenience, they have same `groupId`, versioning and release cycle as core
 | DynamoDB                 | [DynaMap](https://github.com/codanbaru/dynamap) <br> `com.codanbaru.kotlin:dynamap`                                                                      | JVM                     | Allows serialization and deserialization of objects to and from [AttributeValue](https://sdk.amazonaws.com/kotlin/api/latest/dynamodb/aws.sdk.kotlin.services.dynamodb.model/-attribute-value/index.html) of Amazon [DynamoDB](https://aws.amazon.com/dynamodb/)                                                                                                                                                                                           |
 | Bencoding                | [iseki0/kotlinx-serialization-bencoding](https://github.com/iseki0/kotlinx-serialization-bencoding) <br> `space.iseki.bencoding:kotlinx-serialization-bencoding`| JVM, JavaScript  | Allows serialization and deserialization of objects to and from [Bencoding](https://www.bittorrent.org/beps/bep_0003.html#bencoding) of BitTorrent.                                                                                                                                                                                                                                                                                                        |
 | Smile                    | [vooft/kotlinx-serialization-smile](https://github.com/vooft/kotlinx-serialization-smile) <br> `io.github.vooft:kotlinx-serialization-smile-core`        | all supported platforms | Allows serialization and deserialization of objects to and from [Smile](https://en.wikipedia.org/wiki/Smile_(data_interchange_format)).                                                                                                                                                                                                                                                                                                                    |
+| PHP                      | [jsoizo/kotlinx-serialization-php](https://github.com/jsoizo/kotlinx-serialization-php) <br> `com.jsoizo:kotlinx-serialization-php`        | JVM, Android, Native | Allows serialization and deserialization of objects to and from [PHP Serialization](https://www.php.net/manual/en/function.serialize.php).                                                                                                                                                                                                                                                                                                                    |