[doc] Development, localhost, init

[ghost]

I suggest to add a line to the Localhost section in the Readme, that reminds to call

netlifyIdentity.init()

with no parameters when developing on localhost, to trigger the request for the site URL for dev mode

Otherwise, using the APIUrl parameter, the page is redirected to the wrong place, or doesn't work at all if the parameter is set to http://localhost

[jlengstorf]

this should no longer be an issue — please open a new issue (a reproduction or screen recording of the problem would be very much appreciated!) if localhost is causing problems!