docs(operators): add documentation for operator buffer

Add initial version of documentation for transformation operator 'buffer'

Author: natmegs

src/operator-docs/transformation/buffer.ts

@@ -1,6 +1,57 @@
 import { OperatorDoc } from '../operator.model';
 
 export const buffer: OperatorDoc = {
-  'name': 'buffer',
-  'operatorType': 'transformation'
+  name: 'buffer',
+  operatorType: 'transformation',
+  signature: 'public buffer(closingNotifier: Observable): Observable',
+  useInteractiveMarbles: true,
+  parameters: [
+    {
+      name: 'closingNotifier',
+      type: 'Observable',
+      attribute: '',
+      description:
+        'An Observable that signals the buffer to be emitted on the output Observable.'
+    }
+  ],
+  marbleUrl: 'http://reactivex.io/rxjs/img/buffer.png',
+  shortDescription: {
+    description: `
+      Buffers the source Observable values until <span class="markdown-code">closingNotifier</span>
+      emits.
+    `
+  },
+  walkthrough: {
+    description: `
+      <p>
+        Buffers the incoming Observable values until the given
+        <span class="markdown-code">closingNotifier</span> Observable emits a value, at which point
+        it emits the buffer on the output Observable and starts a new buffer internally,
+        awaiting the next time <span class="markdown-code">closingNotifier</span> emits.
+      </p>
+    `
+  },
+  examples: [
+    {
+      name: 'On every click, emit array of most recent interval events',
+      code: `
+        const clicks = Rx.Observable.fromEvent(document, 'click');
+        const interval = Rx.Observable.interval(1000);
+        const buffered = interval.buffer(clicks);
+        buffered.subscribe(x => console.log(x));
+      `,
+      externalLink: {
+        platform: 'JSBin',
+        url: 'http://jsbin.com/xetemuteho/embed?js,console,output'
+      }
+    }
+  ],
+  relatedOperators: [
+    'bufferCount',
+    'bufferTime',
+    'bufferToggle',
+    'bufferWhen',
+    'window'
+  ],
+  additionalResources: []
 };