Include install dependencies step in Release documentation. (#3710)
Include install dependencies step in Release documentation. (#3710)

When walking through the process of building a release for the first time, we've
seen a few people copy these steps out and expect them to run.

On a new server they fail, as `npm install` is not listed.

This causes a "webpack not found" error, which can be confusing (especially to
those without experience with JavaScript and its build process).
rafbgarcia/phoenix,phoenixframework/phoenix,nshafer/phoenix,0x00evil/phoenix,jwarwick/phoenix,0x00evil/phoenix,michalmuskala/phoenix,nshafer/phoenix,eksperimental/phoenix,phoenixframework/phoenix,rafbgarcia/phoenix,nshafer/phoenix,michalmuskala/phoenix,rafbgarcia/phoenix,optikfluffel/phoenix,jwarwick/phoenix,optikfluffel/phoenix,eksperimental/phoenix,0x00evil/phoenix,phoenixframework/phoenix,optikfluffel/phoenix