updating s-project.json

[Carl Hunter-Roach]

although there is generic text at serverless.com it would be nice to have a section on adding this plugin to. I guessed wrong with 'serveless-model' and realised my error. If the really-useful server less-models-plugin is one's first plugin one could over look the need to update

In the file s-project.json add the plug to the list of plug-ins. E.g.,

{
"name": "juturnaSLS",
"custom": {},
"plugins": ["serverless-models-plugin"]
}

[Frank Schmid]

Will update the README. Thank you :-)