Add link from Dockerfile config file to debug usage

docs/source/config_files.rst

@@ -245,5 +245,9 @@ With Dockerfiles, a regular Docker build will be performed.
 .. note::
     If a Dockerfile is present, all other configuration files will be ignored.
 
+If you're working on an existing project and need the `Dockerfile` escape
+hatch, you can :ref:`view the generated Dockerfile
+<usage-debugging-with-debug-and-no-build>`.
+
 See the `Advanced Binder Documentation <https://mybinder.readthedocs.io/en/latest/tutorials/dockerfile.html>`_ for
 best-practices with Dockerfiles.

docs/source/usage.rst

@@ -106,6 +106,8 @@ by ``repo2docker`` to see how to configure the build process.
    :ref:`configuration files <config-files>`.
 
 
+.. _usage-debugging-with-debug-and-no-build:
+
 Debugging repo2docker with ``--debug`` and ``--no-build``
 =========================================================