improve rb/summary/lines-of-code description

Author: alexrford

ql/src/queries/summary/LinesOfCode.ql

@@ -1,9 +1,10 @@
 /**
  * @id rb/summary/lines-of-code
  * @name Total lines of Ruby code in the database
- * @description The total number of lines of Ruby code across all files,
- *   including vendored code, tests. This query counts the lines of code,
- *   excluding whitespace or comments.
+ * @description The total number of lines of Ruby code from the source code
+ *   directory, including external libraries and auto-generated files. This is a
+ *   useful metric of the size of a database. This query counts the lines of
+ *   code, excluding whitespace or comments.
  * @kind metric
  * @tags summary
  */