Merge pull request #10521 from MrMino/debugging_pip_docs

Add a section about debugging to development docs

Author: pradyunsg

docs/html/development/getting-started.rst

@@ -125,6 +125,25 @@ To use linters locally, run:
     readability problems.
 
 
+Running pip under a debugger
+============================
+
+In order to debug pip's behavior, you can run it under a debugger like so:
+
+.. code-block:: console
+
+    $ python -m pdb -m pip --debug ...
+
+
+Replace the ``...`` with arguments you'd like to run pip with. Give PDB the
+``c`` ("continue") command afterwards, to run the process.
+
+The ``--debug`` flag disables pip's exception handler, which would normally
+catch all unhandled exceptions. With this flag, pip will let these exceptions
+propagate outside of its main subroutine, letting them get caught by the
+debugger. This way you'll be able to debug an exception post-mortem via PDB.
+
+
 Building Documentation
 ======================