Change the mobile menu button or ad text

I thanks for your wonderful theme.
When the website is shown in “tablet or mobile mode” the menu becomes a the button with 3 lines in it. Of course, i understand that’s the menu, i love it, however, my customers doesnt always get it, they are adult people who are just realizing the technology, and I want it for them as friendly as possible. I would add a text next to the button that says “Menu” as in the Spacius theme. I am a newbie, I appreciate your help.Thanks