Update README.md
Empty string does not work in the baseUrl for group pages. It results in errors when opening pages of the documentation other than the index. Instead, '/' should be used.
From the documentation of docusaurus:
baseUrl for your site. This can also be considered the path after the host. For example, /metro/ is the baseUrl of https://facebook.github.io/metro/. For URLs that have no path, the baseUrl should be set to /. This field is related to the url field.