[PATCH 1 of 2 evolve-ext] README: document how to run the tests

[Greg Ward]

# HG changeset patch
# User Greg Ward <greg at gerg.ca>
# Date 1397585180 14400
#      Tue Apr 15 14:06:20 2014 -0400
# Node ID a94a4c957ab76ed71974ab7fd3b527472e2b84cc
# Parent  ec4c17e0aee602bd12f3922dcc47bbda0edb8824
README: document how to run the tests

diff --git a/README b/README
--- a/README
+++ b/README
@@ -29,7 +29,12 @@
 ==========
 
 The simplest way to contribute is to issue a pull request on Bitbucket
-(https://bitbucket.org/marmoute/mutable-history).
+(https://bitbucket.org/marmoute/mutable-history). Please don't forget
+to update and run the tests when you fix a bug or add a feature. To
+run the tests:
+
+    cd tests
+    python run-tests.py --with-hg=/path/to/hg
 
 However, some cutting-edge changes may be found in a mutable repository hosted
 by logilab before they are published.