Dev: fixed URLs in README
Dev: fixed URLs in README

The CSS URLs were incomplete (missing `mobile/`).
The JS URL was missing.

Change-Id: I93c4a024421643d53e7c72ebe8167c15d5c7fa6c

wikimedia/mediawiki-services-mobileapps,wikimedia/mediawiki-services-mobileapps,wikimedia/mediawiki-services-mobileapps,wikimedia/mediawiki-services-mobileapps,wikimedia/mediawiki-services-mobileapps,wikimedia/mediawiki-services-mobileapps