Added quick start guide

Author: Alan-Cha

docs/video.svg

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+# OASGraph Quickstart
+
+## Video demo
+
+[![Video demo](../docs/video.svg)](https://www.youtube.com/watch?v=_u7artgCqAw&feature=youtu.be)
+
+## Write up
+
+### Start API server
+
+In your LoopBack application, run the following command.
+
+```
+npm start
+```
+
+***
+
+Or boot up whichever backend that supports your API.
+
+### Save the OAS
+
+In your Loopback application, go [here](http://localhost:3000/openapi.json).
+
+***
+
+Or get whichever OAS you would like to use.
+
+
+### Clone OASGraph
+
+You can find the repository [here](https://github.com/strongloop/oasgraph).
+
+```
+git clone [email protected]:strongloop/oasgraph.git
+```
+
+### Create CLI tool
+
+Go into the OASGraph directory...
+
+```
+cd oasgraph
+```
+
+... and build the CLI tool.
+
+```
+npm link
+```
+
+### Start GraphQL server
+
+```
+oasgraph [OAS path]
+```
+
+To see your GraphQL server, go [here](http://localhost:3001/graphql).