Document karva.raises context manager

docs/usage/functions.md

@@ -49,3 +49,41 @@ def test_function2():
 Then running `uv run karva test` will result in two test fails.
 
 You can still use `pytest.fail()` to fail tests.
+
+## Raises
+
+If you want to assert that a block of code raises a specific exception, use `karva.raises()`.
+
+```python title="test.py"
+import karva
+
+def test_function():
+    with karva.raises(ValueError):
+        raise ValueError("something went wrong")
+```
+
+You can optionally provide a `match` parameter to match a regex pattern against the string representation of the exception.
+
+```python title="test.py"
+import karva
+
+def test_function():
+    with karva.raises(ValueError, match="something"):
+        raise ValueError("something went wrong")
+```
+
+You can access the exception info by using the `as` keyword. The returned object has `type`, `value`, and `tb` properties.
+
+```python title="test.py"
+import karva
+
+def test_function():
+    with karva.raises(ValueError) as exc_info:
+        raise ValueError("something went wrong")
+
+    assert exc_info.type is ValueError
+    assert str(exc_info.value) == "something went wrong"
+    assert exc_info.tb is not None
+```
+
+You can still use `pytest.raises()` to assert exceptions.