Create node-red-extra.sh

I have created this script to reduce manual effort to install extra node-red nodes. Copy this shell script in Node-RED top-level root directory.
GIve permission to be executable by doing $chmod +x node-red-extra.sh
Extra Node list and details can be found in this link : https://github.com/node-red/node-red-nodes
[for Unix and Unix like system ie. Linux only]