Incorrect instructions on where/how to add custom plugins

[wilsonmar]

Can we add a reference to https://github.com/nasa/openmct-hello
getting started instructions at https://nasa.github.io/openmct/
That page currently has too simplistic instructions:

1. CLONE THE SOURCE CODE
git clone https://github.com/nasa/openmct.git
2 INSTALL DEVELOPMENT DEPENDENCIES
npm install
3 RUN A LOCAL DEVELOPMENT SERVER
npm start

npm install results in an install of a version not supported.

Even after figuring out workaround to install v20,
the web page displays with no metrics displayed.

Should we fork the repo so we have a way to store our plugin changes?
Or should we create another repo and copy the files to openmct?