Mention pytest_enter_pdb in the docs

_pytest/hookspec.py

@@ -291,4 +291,6 @@ def pytest_exception_interact(node, call, report):
     """
 
 def pytest_enter_pdb():
-    """ called upon pdb.set_trace()"""
+    """ called upon pdb.set_trace(), can be used by plugins to take special
+    action just before the python debugger enters in interactive mode.
+    """

doc/en/writing_plugins.rst

@@ -501,7 +501,7 @@ reporting or interaction with exceptions:
 .. autofunction:: pytest_internalerror
 .. autofunction:: pytest_keyboard_interrupt
 .. autofunction:: pytest_exception_interact
-
+.. autofunction:: pytest_enter_pdb
 
 
 Reference of objects involved in hooks