add tracker scrape example

Author: feross

examples/tracker-scrape.md

@@ -0,0 +1,43 @@
+# Count the number of peers using the `scrape` feature of torrent trackers
+
+Here's a full example with `browserify`.
+
+```
+npm install browserify parse-torrent bittorrent-tracker
+```
+
+`scrape.js`:
+
+```js
+var Tracker = require('bittorrent-tracker')
+var magnet = require('magnet-uri')
+
+// These values don't matter
+var peerId = new Buffer('01234567890123456789')
+var port = 6889
+
+var magnetURI = "magnet:?xt=urn:btih:6a9759bffd5c0af65319979fb7832189f4f3c35d&dn=sintel.mp4&tr=udp%3A%2F%2Fexodus.desync.com%3A6969&tr=udp%3A%2F%2Ftracker.coppersurfer.tk%3A6969&tr=udp%3A%2F%2Ftracker.internetwarriors.net%3A1337&tr=udp%3A%2F%2Ftracker.leechers-paradise.org%3A6969&tr=udp%3A%2F%2Ftracker.openbittorrent.com%3A80&tr=wss%3A%2F%2Ftracker.btorrent.xyz&tr=wss%3A%2F%2Ftracker.fastcast.nz&tr=wss%3A%2F%2Ftracker.openwebtorrent.com&tr=wss%3A%2F%2Ftracker.webtorrent.io&ws=https%3A%2F%2Fwebtorrent.io%2Ftorrents%2Fsintel-1024-surround.mp4"
+
+var parsedTorrent = magnet(magnetURI)
+var client = new Tracker(peerId, port, parsedTorrent)
+
+client.scrape()
+
+client.on('scrape', function (data) {
+  console.log(data)
+})
+```
+
+Bundle up `scrape.js` and it's dependencies into a single file called `bundle.js`:
+
+```bash
+browserify scrape.js -o bundle.js`
+```
+
+`index.html`:
+
+```js
+<script src="bundle.js"></script>
+```
+
+Open `index.html` in your browser.