Add nvm to installation guide for avm

[shawazi]

Problem

When following the getting started guide on a fresh system, anchor init results in OS errors, and package.json and tests directory fails to be created. nvm, node, and npm must be listed as dependencies as well in order for anchor init to generate the package.json and tests directory.

Solution

npm is a necessary dependency for avm, so it should be listed alongside the other dependencies, I think.