[Archiver] comment for a confusing line

src/Composer/Package/Archiver/BaseExcludeFilter.php

@@ -140,6 +140,7 @@ abstract class BaseExcludeFilter
             $pattern .= '/';
         }
 
+        // remove delimiters as well as caret (^) from the regex
         $pattern .= substr(Finder\Glob::toRegex($rule), 2, -1);
 
         return array($pattern . '#', $negate, false);