Button for underlining text

[erichjsonfosse]

Hi,

First of all, thanks for an awesome extension! It has really come in handy 💯

It does seem like it's missing the button for underlining text, tho. Is there a way for me to contribute to having it added?

[formfcw]

Thank you for your interest!

Feel free to contribute. Here is a comment about adding extensions: #27 (comment)