Update read me file to include how to run the internal dev server, Fixes T608

Summary: - Update readme to include `gulp nodeserver`

Test Plan: - Read the README file. Look out for the part about running the internal web server

Reviewers: rjmackay

Reviewed By: rjmackay

Subscribers: shadowhand

Maniphest Tasks: T608

Differential Revision: https://phabricator.ushahidi.com/D276