Add msgspec to implementations

Author: jcrist

implementations.md

@@ -155,6 +155,7 @@ For example, the only incompatibilities between draft-04 and draft-06 involve `e
     -   [typescript-json-schema](https://github.com/YousefED/typescript-json-schema)
 -   Python
     -   [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.
 -   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