1) click on the "chain" icon in the row of tools you see above your signature/reply (ninth icon from left)
2) in the URL row, paste keepyourfeetinthestreet.com
3) in the Text row, you have the option of covering "keepyourfeetinthestreet.com" with a text. What will be seen is the text, but the text will open to keepyourfeetinthestreet.com. But you can just keep the URL without a text.
4) click on Insert