Add missing File reference to the docs

As related in #7696

doc/en/reference.rst

@@ -784,12 +784,19 @@ ExceptionInfo
     :members:
 
 
-pytest.ExitCode
-~~~~~~~~~~~~~~~
+ExitCode
+~~~~~~~~
 
 .. autoclass:: _pytest.config.ExitCode
     :members:
 
+File
+~~~~
+
+.. autoclass:: _pytest.nodes.File()
+    :members:
+    :show-inheritance:
+
 
 FixtureDef
 ~~~~~~~~~~

src/_pytest/nodes.py

@@ -542,7 +542,10 @@ class FSCollector(Collector):
 
 
 class File(FSCollector):
-    """Base class for collecting tests from a file."""
+    """Base class for collecting tests from a file.
+
+    :ref:`non-python tests`.
+    """
 
 
 class Item(Node):