Add lines-of-code clarification

Author: Illia Romanenko

lib/analysis_options.yaml

@@ -26,7 +26,9 @@ dart_code_metrics:
 
     # McConnell, S. (2004), Chapter 7.4: High-Quality Routines: How Long Can a Routine Be?. Code Complete, Second Edition, Redmond, WA, USA: Microsoft Press. 173-174
     source-lines-of-code: 200
-#    lines-of-code: 50
+
+    # We use source-lines-of-code instead of this as we don't want to count comment or blank lines.
+    # lines-of-code: 50
   rules:
     - avoid-late-keyword
     - avoid-non-null-assertion