Add more detailed dev installation instructions

[heisencoder]

I'm running on Linux, but am having trouble running simple commands like make dev. It looks like there are a lot of packages that need to be added first. Here are some notes from my experience that may be suitable for being appended to the README.md.

Here are the things I needed to run to set things up:

sudo apt install jq ruby npm
sudo npm install -g @vue/cli
sudo npm install -g @vue/cli-service
sudo npm install -g @vue/cli-plugin-babel
sudo npm install -g @vue/cli-plugin-unit-mocha
sudo npm install filemanager-webpack-plugin
make dev

After this was complete, I was able to visit chrome://extensions/ in Chrome, click "load unpacked", and then point to the package subdirectory.