install changes

Ahoy! Here are some changes I made based on installation notes I took while installing Marvin on my BeagleBone this weekend. I added some details about which Ubuntu to use on the BBB, system dependencies, how to build node & golang. I also added web/package.json for installing needed node modules locally, and made sure that the bin path where they are installed is added to the PATH. I also added some default marvin.json and marvin.conf files to conf.