Update R-Shiny docs

[chuckbelisle]

Tracking changes to the documentation for the R-Shiny dashboard

[blairdrummond]

CC @ca-scribner

We should remove the reliance on shiny/PACKAGES that we currently use and use a dependencies.R file in the dashboard folder. Example. Then we can remove reference to the shiny repo in our documentation. (This might also simplify the testing process)

Then we should lay out the PR process in more detail; i.e.

1. Fork the repo https://github.com/StatCan/R-dashboards
2. Add a new folder with your dashboard
3. Make sure that the folder has ui.R, server.R, and dependencies.R (provide an example and use install.packages(package_name))
4. Submit the Pull Request, and Tag the DAaaS team.

[Souheil-Yazji]

Shiny dash feat removed