showstack: add an extension docstring
Now, running `hg help showstack` will give details on how to use the extension.
--- a/contrib/showstack.py Mon Jan 15 10:44:49 2018 +0000
+++ b/contrib/showstack.py Sun Dec 10 21:42:33 2017 +0100
@@ -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