Omnitrace sample documentation (#179)

* Documentation for omnitrace-sample

* Improve omnitrace-sample

- improve the printing of the env updates
- remove env settings when something is deactivated
- restore env settings when something is deactivated

source/docs/runtime.md

@@ -1,4 +1,4 @@
-# Customizing Omnitrace Runtime
+# Configuring Omnitrace Runtime
 
 ```eval_rst
 .. toctree::