docs: add some documentation

docs/examples/dataclasses_stdlib_inheritance.py

@@ -0,0 +1,26 @@
+import dataclasses
+
+import pydantic
+
+
+@dataclasses.dataclass
+class Z:
+    z: int
+
+
+@dataclasses.dataclass
+class Y(Z):
+    y: int = 0
+
+
+@pydantic.dataclasses.dataclass
+class X(Y):
+    x: int = 0
+
+foo = X(x=b'1', y='2', z='3')
+print(foo)
+
+try:
+    X(z='pika')
+except pydantic.ValidationError as e:
+    print(e)

docs/usage/dataclasses.md

@@ -57,6 +57,14 @@ them with `pydantic.dataclasses.dataclass`.
 ```
 _(This script is complete, it should run "as is")_
 
+Stdlib dataclasses (nested or not) can also be inherited and _pydantic_ will automatically validate
+all the inherited fields.
+
+```py
+{!.tmp_examples/dataclasses_stdlib_inheritance.py!}
+```
+_(This script is complete, it should run "as is")_
+
 Bear in mind that stdlib dataclasses (nested or not) are **automatically converted** into _pydantic_ dataclasses
 when mixed with `BaseModel`!