[PATCH] showstack: add an extension docstring

[Boris Feld]

# HG changeset patch
# User Boris Feld <boris.feld at octobus.net>
# Date 1512938553 -3600
#      Sun Dec 10 21:42:33 2017 +0100
# Node ID bff8fba926e22982e6b5be544fc36e1e16cedfdd
# Parent  ebf14075a5c113f4fea6e89a4394d8c8fc9e6935
# EXP-Topic showstack-doc
# Available At https://bitbucket.org/octobus/mercurial-devel/
#              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r bff8fba926e2
showstack: add an extension docstring

Now, running `hg help showstack` will give details on how to use the extension.

diff --git a/contrib/showstack.py b/contrib/showstack.py
--- a/contrib/showstack.py
+++ b/contrib/showstack.py
@@ -1,6 +1,8 @@
 # showstack.py - extension to dump a Python stack trace on signal
 #
 # binds to both SIGQUIT (Ctrl-\) and SIGINFO (Ctrl-T on BSDs)
+"""dump stack trace when receiving SIGQUIT (Ctrl-\) and SIGINFO (Ctrl-T on BSDs)
+"""
 
 from __future__ import absolute_import
 import signal