NET-920 Modify rule S125: Add dotnet example

rules/S125/csharp/rule.adoc

@@ -1,4 +1,40 @@
-include::../rule.adoc[]
+== Why is this an issue?
+
+Commented-out code distracts the focus from the actual executed code. It creates a noise that increases maintenance code. And because it is never executed, it quickly becomes out of date and invalid.
+
+Commented-out code should be deleted and can be retrieved from source control history if required.
+
+== How to fix it
+
+Delete the commented out code.
+
+=== Code examples
+
+==== Noncompliant code example
+
+[source,csharp,diff-id=1,diff-type=noncompliant]
+----
+void Method(string s)
+{
+    // if (s.StartsWith('A'))
+    // {
+    //     s = s.Substring(1);
+    // }
+
+    // Do something...
+}
+----
+
+==== Compliant solution
+
+[source,csharp,diff-id=1,diff-type=compliant]
+----
+void Method(string s)
+{
+    // Do something...
+}
+----
+
 
 ifdef::env-github,rspecator-view[]