[ci skip] Fix example in active_record_basics.md doc (rails#52770)

The example code is:

    Book.find_by(title: "Metaprogramming Ruby 2") 

Instead of:

     Book.find_by(author: "J.R.R. Tolkien") 

Also add comments in SQL to make it clearer which calls create the queries.

Co-authored-by: Petrik de Heus <[email protected]>

Author: p8

guides/source/active_record_basics.md

@@ -493,8 +493,10 @@ book = Book.find(42)
 The above resulting in this SQL:
 
 ```sql
-SELECT "books".* FROM "books" WHERE "books"."author" = ? LIMIT ?  [["author", "J.R.R. Tolkien"], ["LIMIT", 1]]
+-- Book.find_by(title: "Metaprogramming Ruby 2")
+SELECT "books".* FROM "books" WHERE "books"."title" = ? LIMIT ?  [["title", "Metaprogramming Ruby 2"], ["LIMIT", 1]]
 
+-- Book.find(42)
 SELECT "books".* FROM "books" WHERE "books"."id" = ? LIMIT ?  [["id", 42], ["LIMIT", 1]]
 ```