Add thank you to YourKit to the main project page. (#341)

* In order to obtain free open source YourKit license we are asked to put the link to YourKit website.

Signed-off-by: Abdelhamid Bakhta <abdelhamid.bakhta@consensys.net>

README.md

@@ -45,3 +45,14 @@ Instructions for how to get started with developing on the Besu codebase. Please
 ## Release Notes
 
 [Release Notes](CHANGELOG.md)
+
+## Special thanks
+YourKit for providing us with a free profiler open source license. 
+
+YourKit supports open source projects with innovative and intelligent tools
+for monitoring and profiling Java and .NET applications.
+YourKit is the creator of <a href="https://www.yourkit.com/java/profiler/">YourKit Java Profiler</a>,
+<a href="https://www.yourkit.com/.net/profiler/">YourKit .NET Profiler</a>,
+and <a href="https://www.yourkit.com/youmonitor/">YourKit YouMonitor</a>.
+
+![YourKit Logo](https://www.yourkit.com/images/yklogo.png)