[simple] README clarification on pooled transaction

[henrymcl]

Please consider adding the comments below for README's Transactions part.

connection.beginTransaction(function(err) {
  if (err) { throw err; }
  connection.query('INSERT INTO posts SET title=?', title, function (error, results, fields) {
    if (error) {
      return connection.rollback(function() {
        // remember to connection.release() if it's pool connection
        throw error;
      });
    }

    var log = 'Post ' + results.insertId + ' added';

    connection.query('INSERT INTO log SET data=?', log, function (error, results, fields) {
      if (error) {
        return connection.rollback(function() {
          // remember to connection.release() if it's pool connection
          throw error;
        });
      }
      connection.commit(function(err) {
        if (err) {
          return connection.rollback(function() {
            // remember to connection.release() if it's pool connection
            throw err;
          });
        }
        // remember to connection.release() if it's pool connection
        console.log('success!');
      });
    });
  });
});

[dougwilson]

Hello, and thank you for the suggestion. There is no requirement to release the connection back to the pool if there is an error in those locations. You can make more queries if you want; when to release is very dependent on your application. Adding those comments would be misleading.