docs: update readme for attaching containers

docs/dev.rst

@@ -84,6 +84,21 @@ Finally, the platform can also be started back up with ``launch``. It will take
 
   tutor dev launch --pullimages
 
+Debugging with breakpoints
+--------------------------
+
+To debug a local edx-platform repository, add a `python breakpoint <https://docs.python.org/3/library/functions.html#breakpoint>`__ with ``breakpoint()`` anywhere in the code. Then, start the container by running ``start -d`` followed by the service's name and attach to the container by running ``attach`` followed by the service's name::
+
+  # Debugging LMS:
+  tutor dev start -d lms
+  tutor dev attach lms
+
+  # Or, debugging CMS:
+  tutor dev start -d cms
+  tutor dev attach cms
+
+To detach from the container without shutting it down, use ``Ctrl+p`` followed with ``Ctrl+q``.
+
 Running arbitrary commands
 --------------------------