Add link to Brendan Gregg's perf-tools repo

README.md

@@ -560,6 +560,7 @@ Comparison of NoSQL servers: http://kkovacs.eu/cassandra-vs-mongodb-vs-couchdb-v
 
   + [grml](https://grml.org) – bootable Debian Live CD with powerful CLI tools.
   * [mitmproxy](http://mitmproxy.org/) - A Python tool used for intercepting, viewing and modifying network traffic. Invaluable in troubleshooting certain problems.
+  * [perf-tools](https://github.com/brendangregg/perf-tools) - Performance analysis tools based on Linux perf_events (aka perf) and ftrace.
   * [Sysdig](http://www.sysdig.org/) - Capture system state and activity from a running Linux instance, then save, filter and analyze.
   * [Wireshark](http://www.wireshark.org/) - The world's foremost network protocol analyzer.