Add drf-jsonschema-serializer schema generator

Author: sergei-maertens

implementations.md

@@ -157,6 +157,7 @@ For example, the only incompatibilities between draft-04 and draft-06 involve `e
     -   [Pydantic](https://pydantic-docs.helpmanual.io/) (MIT) - generates schemas from Python models based on Python 3.6+ type hints.
     -   [msgspec](https://jcristharif.com/msgspec/) (BSD-3-Clause) - generates schemas from Python type annotations.
     -   [mashumaro](https://github.com/Fatal1ty/mashumaro) (Apache 2.0) - generates schemas from Python type annotations
+    -   [drf-jsonschema-serializer](https://github.com/maykinmedia/drf-jsonschema-serializer) (BSD-3-Clause) - generates schemas from Django Rest Framework serializers
 -   Java
     -   [jsonschema-generator](https://github.com/victools/jsonschema-generator) (Apache 2.0) - generates schemas from Java types *supports Draft 7 and Draft 2019-09*
 -   Scala