Corrected buildtree_runner/README.md by puttting 'sudo' in front of...

Corrected buildtree_runner/README.md by puttting 'sudo' in front of ./recreate_buildtree_running_environment.sh

continuousintegration/buildtree_runner/README.md

@@ -66,7 +66,7 @@ MHVTL should then be setup by running:
 
 ```
 cd ~/CTA/continuousintegration/buildtree_runner
-./recreate_buildtree_running_environment.sh
+sudo ./recreate_buildtree_running_environment.sh
 ```
 
 ### Preparing the test instance