OK, this seemed to work for me. Go into a directory outside of .node-red (I used my home directory ~) then
git clone https://github.com/bartbutenaers/node-red-web-nodes
Which downloads those nodes to the folder node-red-web-nodes under wherever you are. Then go into node-red-web-nodes/dropbox and run
npm install
Then go back to .node-red and run
npm install your_folder/node-red-web-nodes/dropbox
Then restart node-red and refresh the browser.
So for me on linux I did
cd ~
git clone https://github.com/bartbutenaers/node-red-web-nodes
cd node-red-web-nodes/dropbox
npm install
cd ~/.node-red
npm install ~/node-red-web-nodes/dropbox
node-red-stop;node-red-start
and refresh the browser. Do not delete the node-red-web-nodes folder.
[Edit] Once it has been released to npm then
npm remove node-red-node-dropbox
npm install node-red-node-dropbox
and you can delete the node-red-web-nodes folder.