Emphasize realization-0 executed only

Author: andreas-el

src/ert/run_models/single_test_run.py

@@ -18,7 +18,7 @@ class SingleTestRun(EnsembleExperiment):
     Single test is equivalent to EnsembleExperiment, in that it
     samples the prior and evaluates it.<br>There are two key differences:<br>
     1) Single test run always runs locally using the <b>local queue</b><br>
-    2) Only a <b>single realization</b> is run<br>
+    2) Only a <b>single realization</b> (realization-0) is run<br>
     """
 
     def __init__(