Updating documentation on running gulp.

[dzink]

There are a few additional troubleshooting tasks I used to get gulp running on my local machine, which I have documented here.

@tortillaj sorry for the double tags - not sure if 'needs doc update' is a response from the reviewer, or a tag to let the reviewer know this is a documentation PR.

[tortillaj]

@dzink I don't think this documentation belongs in this repo. We track bear_skin docs over in its own repo: https://github.com/zivtech/bear_skin
In fact I'm kind of confused about why any bear_skin docs are here. Of course, it's totally fine to leave it, but someone will need to periodically keep it in sync.