docs: removes npx info & moves src link up (#4972)

FIXES: #4970 

confirmed rest of instructions work so left them in, even though duplicate of guide over at Material UI. thoughts?

examples/with-material-ui/README.md

@@ -1,45 +1,3 @@
-[![Deploy to now](https://deploy.now.sh/static/button.svg)](https://deploy.now.sh/?repo=https://github.com/mui-org/material-ui/tree/master/examples/nextjs)
 # Material-UI example
 
-## How to use
+Source code is hosted on the [Material-UI](https://github.com/mui-org/material-ui/tree/master/examples/nextjs) repository.
-
-### Using `create-next-app`
-
-Execute [`create-next-app`](https://github.com/segmentio/create-next-app) with [Yarn](https://yarnpkg.com/lang/en/docs/cli/create/) or [npx](https://github.com/zkat/npx#readme) to bootstrap the example:
-
-```bash
-npx create-next-app --example with-material-ui with-material-ui-app
-# or
-yarn create next-app --example with-material-ui with-material-ui-app
-```
-
-### Download manually
-
-Download the example:
-
-```bash
-curl https://codeload.github.com/mui-org/material-ui/tar.gz/master | tar -xz --strip=2  material-ui-master/examples/nextjs
-cd nextjs
-```
-
-Install it and run:
-
-```bash
-npm install
-npm run dev
-# or
-yarn
-yarn dev
-```
-
-Deploy it to the cloud with [now](https://zeit.co/now) ([download](https://zeit.co/download))
-
-```bash
-now
-```
-
-## The idea behind the example
-
-This example features how you use [material-ui](https://github.com/mui-org/material-ui) (Material components that implement Google's Material Design) with Next.js.
-
-:warning: The source code [is hosted](https://github.com/mui-org/material-ui/tree/master/examples/nextjs) on the Material-UI repository.