Update readme for menus/location endpoint

[petertenhoor]

Hi there,

Just a small suggestion for your readme.md documentation. The endpoint below "Menus from location (theme location)" seems to be incorrect. It should be:

better-rest-endpoints/v1/menus/location/{menu-slug}

Thanks for this nice plugin :)

[erwstout]

Thanks for the heads up. I'm pretty swamped right now so if you want to submit a quick PR i can get that merged in. Thanks!