You must first understand who your resume is for. For what?
Your resume is for HR, in order to promote yourself and get an interview.
From the standpoint of HR, they have a lot of work to deal with every day, and the time to read each resume may not exceed 10 second, just a quick glance. Adding a resume cover outside your resume is equivalent to putting your resume in a box and giving it to HR. Do you think he has the time and patience to open it?
I suggest that you might as well spend more time on the production of your resume, highlight the key points and show your advantages.