Readme: Add release/changelog link

Signed-off-by: Martin Thoma <info@martin-thoma.de>

Author: MartinThoma

README.md

@@ -594,3 +594,8 @@ for family in text_string_to_metric_families(u"my_gauge 1.0\n"):
   for sample in family.samples:
     print("Name: {0} Labels: {1} Value: {2}".format(*sample))
 ```
+
+## Links
+
+* [Releases](https://github.com/prometheus/client_python/releases): The releases page shows the history of the project and acts as a changelog.
+* [PyPI](https://pypi.python.org/pypi/prometheus_client)