Adding comment again as asked by the author

KrustyHack · KrustyHack · commit 25b81f1ce0ac · 2015-04-15T17:25:06.000+02:00
diff --git a/README.md b/README.md
@@ -378,7 +378,7 @@ Trivial (ba)sh alternatives:
 when-up
 -------
 
-Waits until a given host is online
+Waits until a given host is online (determined by ping until executing a given command)
 
 Example:
 
