Update README link to monorepo

[markmhendrickson]

It should got to https://github.com/blockstack/ui/tree/feat/monorepo

[iamnishanbhandari]

The issue could be due to the specific font size value that is being provided. If the font size value is not valid or if it conflicts with other styles or settings, it may result in the font size being ignored. I would be interested in working on this issue. Could someone please assign it to me?