To add additional text under Header button, you can use this code to Website Tools > Custom CSS.
a.btn:after {
content: "Click here to get started";
font-size: 12px;
color: #fff;
display: block;
}

Result

To add additional text under Header button, you can use this code to Website Tools > Custom CSS.
a.btn:after {
content: "Click here to get started";
font-size: 12px;
color: #fff;
display: block;
}

Result
