Change some mercurial/ hg.python.org references. (#8)

diff --git a/Tools/importbench/README b/Tools/importbench/README
index 81a5544..6ba386c 100644
--- a/Tools/importbench/README
+++ b/Tools/importbench/README
@@ -3,4 +3,4 @@
 It should not be used as an overall benchmark of import performance, but rather
 an easy way to measure impact of possible code changes. For a real-world
 benchmark of import, use the normal_startup benchmark from
-hg.python.org/benchmarks.
+https://github.com/python/performance