Your template is fine as a letter offering employment. If it’s actually an employment contract, you should include all of the other key terms of employment, including sick days, stat holidays, bonuses, etc. You don’t necessarily have to spell them out in the document. You can just indicate that the employee has received and acknowledged the terms as set out in your HR policies and attach a copy as an exhibit to the agreement. You can also do the same thing for Code of Conduct.